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·KALPOMDATIONS OF WOOD BOLOGY
The Colby Cal ? Seuson
Cetteler Mey ad Hockey hD Wall
Hudy by Drold Boot
Adaptetlen, Bruce Welce nd Adrien Verb
Aled Growth and Development, by Mories S
Art Thrillery by Ke Sath box
Anal Diretty by La D Hardon
Abd kalorier by Vau Dathule and that Stella
The Life of the Bron Mut by Arthur W Colton
The Part Dept, Ly Barold C. Bol
Mo Katar Katow Betu

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·POUNDATIONS OF MODUAN BIOLOGY $

·Heredity
DAVID M
BONNER
Umocratty of California Sen Diego
PRENTICE HALL OF INDIA (PRIVATE) UMITED
HEW DELHI

·Here Doord v tom METKEHAL VER TINAL M VIKEHL E TON VL ITKE HALL OF SIL LT METICE AL Or VADA DT MITKE AL L HIMCI OD PE TK AL AL 04 VLTKO $ W. Tuy O ME TICE HALL VOCA farw by Menu der RA mit TKTHALL VE 1 CE HALL OF DU MU TE UWITE That there the um mew Prep in function et Di ME NETICHHALL MOUNDATIO18 07 MODELN HOLOOY SAKIT WILT D McElroy and Carl P SWEDXn, Editor Dua by Water Blub Drop by fda Coop ·The science of blology today is not the same odenco of fifty turonty-five, or oren ten you go Todays acrelented peco of research, akded bow tatud algae, ad paring of view imperts to Hology i npidly chung mog chancter us dbcoveries ple one on top of the other All of us ar mare, borter that cach Dow bod important discovery k bot at a nero addition to our knowledge It abo throm our established beliefs into question, md forces m constantly to reappribe and often to roape the foundations upon which bology rests. An adequate pret entation of the dynamic state of modern biology I, therefore, u formidable task and I challenge worthy of our best teachers, The author of this seda believe that 1 new approach to the organization of the mbject matter of btology ts urgently neodod to meet this challenge, approach that to troduces the stadiont to holog sa grow ing, active dence, aod that ako pents cach teacher of btalog to determine the lead and the trutture of the CTT Cam. anglo trdboot cannot provide soch flerball Ity tod it is the ruthors strong conviction that these student poods mod toucher prorogatires an best be met by 1 roles of short frapeostve, written, in well- Illustrated boobs po planned to encompass those arou of study central to in under standing of the comtent, state, sod direction of modern biology The FOUNDATIONS OF SIODEAN BIOLOGY SERIES repro seats the translation of these kaus foto print, with auch volutne belog complete in Itsel ya at the sure the serving # foteenal part of the kilo 4. bole. Foundations of Modern Biology Series

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·1 3 "For efter all, my cheer sir the chicken may merely bo to go wny of making mother og in thbs book, the tuthor wishes to pay tributo and off his gratitudo to the mechanism chosen by the ofg to repleath its ktod, for this mochankan hu much to do with beredity The study of beredity is to its Infancy but it has already establnbod twelf u a denoo in its own right--the science of genetla. Within this field, we can add do formulate hypotheses, mako prodictions, and subject them to go on tort-que- Hitative aperiments Young ito, bat go peties baus already attitcted the attention of many glont and be the first of the biological sciences to copy the concerted efforts of biologists, choonists, md phytheists. Lice all actonces, gencties has many fucot It dal with the practical problems of foods and drugs, of intelligence and bo- Preface havior and the emploutro problems of popolation. In fact, rectia intrudos in an wallos of hfe Its tovestigaton bave dtverto fotoost od wptrations, yot through them I runs a common thread, an tatenso co rosity about genetic metedolits daturo, Its potentialities, and its member of trans misstan. In the field of heredity thera ure many points of view for the science b bory on many fronts. My colleagues my wall cry to anguish at the bloed vors to this pret entation. But so brief a book on the rubject motor abitrery decidons fperitable, and bere we elect to deco opo uspect that biodi genetidst of all pertadoos topoibet -the gene and what ft doea. While the decision of berodity in thk mhume te centered Cound the me 5 ·Profach genetia tmploges on all aspects of blology on physiology biochemistry grovth and development, structure mod function, to nemno only a few These are fields covered by tho other boole of this series, and we urge that they bo read, for armed with more attenstvo Loowledge of modem Wology you will be able to enrich your understanding of the many skdod field of heredity Writing, Ilo heredity requiret genes The author: genetic ondor moat in writing to modost, but luchtly he enjoyr generous and ablo col leagues. In the planning and writing of this book, the collaboration of thoro colleagues, opecally of Dr Stanloy E Mils, und the editorial udutance of Juma M Gulber Jr was invaluable and the author is in debted to them for whatover carlty sophistication, and polish the volume portos Daold Bi Bonner

·The Material lasis of Horedity
PI
THE CELULAR ELEMENTS
HITOSIS
METOSIS
2
DNA. The Gustle Material
TRANSFOLATION
LACTEMAL MAUSES
INFECTIYE INA
Contents
3
Games ood Blocbralcat Reactions
Pep 15
NEUROSORA UFE CYCLE
THE INHERITANCE TEST
IN NEUROSCOLA
KANOOM ASSORTMENT
LENTED CONES
MUTATION
CINES AND NUTRITION
GUS AND ROCHELOCAL REACTIONS

·4
Genus ad Eurydes
TATTOMAR SYNTHETASE
DETECTINO CAM
TASE CAM
MOTENS
EAZYME ALTERATION
ANGERPRINTING
5
Gees la Actor
lege u
THE STRUCTURE OF DNA
THE WATSON-CRICK MODEL
REMLICATION
CRYPTOGRAPHY
MUTATION
MESSENGER AMA
6
The Molecular Structure of a Gece
la 34
BREAKAGE FUSION
COPY CHOICE
ANE STRUCTULE
COMPLEMENTATION
SUMMARY

·7
Gute Mechanisms
l'epr 03
MUTATION AND SRECTION
LACTERLAL RECOMANATION
DIPLOIDY
DOMINANCE
THIONE
NINETHLETHREONT
UNKAGE
SEX DETERMINATION
8
Gent and Man
14 75
THE CHROMOSOMAL LAAS
OP OENG TRANSMISSION
SOME CONGENITAL DELASES
AND NONDISJUNCTION
PHONYUKETONURLA
SICKLE.CAL ANGOLA
MULTIFU ALLALES
SKIN COLOR
9
0++ and Denlopart
ACQUIRED TATS
CYTOPLASWTC DHERITANC!
SEIRA

·10
Heredity and Hiroshima
len 100
Selected Readlags
Per las
Index
Typ 100

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·The word heredity is simply the same given to the moans by which llytog organisms it produce thedi bod. An udarunding of heredity therefore, requires kooslogo of the various procones truvolved in toproduction. In recent years, this boowl odgo hu tocrousod dramatically Tho combined efforts of an over cong number of research schentlets, and tho dovelopmoet of now tools and apart mental techniques of great porrar havo already revealed moch, and promiso more. Marry questions that hevo pooled gwortious of biologists have been o merod. Moro important, however now fuformation has brod now quortiont, prorokod. dentro for cooper love of com prehension Today with the descriptivo donants of reproduction largely clothed and behind us, we aro gotng after the very atoms of heredity Wo want to know about that armgerpent, tetr architeoture and ther activities, the chemical transformations and the physical forces that provide for the conttatuation of life. Wo can begta by Doting fact ob vion to all of us. Liitot syutems oro highly compla For comple, the most clanetary studies soon reveal tho woulth of biochemical activities that coll dret cootrin fost to survive Yet we also mom from everyday observation that auch or genfon must be not only the means to zaintain, Hall be afrater in to productog ytterns bio ibefs well. Tho best videoco mallable today Indiauta The Material Basis of Heredity that ahke trent limited 1 ·The Matenad Bout of Heroty of substants which to purod on from one generation to the next dod whicha ta large aswe prescribes the nature of the mucceeding generation Those substances wo refer to as the material basis of heredity The scientifc study of the materid buss of beredity begro to the latter part of the nineteroth century with the work of the Austrian monk, Gregor Mendel His esperimental results led him to the formulation of How of heredity widch, in turn, provided the inspiration for the Itsearch that coatirrues at an accelerated pace today Of great current Interest is the fact that recent work in this field has brought about a revolation in modan experimental béology has led to the development of what is not known as molecular biology for which the disciplines of btology chemistry and physics buve fused to create a field of cullango und ercitement. It is the field that shows explotive experimental activity at the present time mod it is the authors biss that malecular btology offert the best opportunity for prining tasight into the basic problems of biology as they are sow defined Hessee the present discussion of heredity all bo centered round the developments of recent years, developments ustas * capertinental tools microorganismis rather than higher plants or higher andrals. Our hope is that in this works # will be possible to aoly to present clomsty the principles anderlying the science of beredity Lou genetics but a tho samo tose to give some toslgbt tnto the problems of the present and the fascination of the future. Th. Calhikest Elegant All organisms onlist of cols. Morrone whether they coutist of ono cell or of thousands, they grow and reprodoco by cell division A buc terium b singlo coll. It grom und it has doubled to store then reproduce by splitting in two. The result of this division to Idendal cell from one. Man is a multicellular organlı and he too grows by bcTERLO cell who and dirtion of bu constituent cello. Ho reprodaces by prodoc ing certain cells (gemetes) sperm (male) and egg (female) which fase to give rise to a Hagle fertilized egg cell (Zygote) The tygoto s otpablo of growing and dividing, and of ultimately pving nx to a new multicellu lær bodividual. The information needed to reproduco a complex mltcellu la todividual u thus timmitted through a single cell mm mach dividing cell la tum must contain the faformation required to reproddee tself Tbo olemoot of baedity bekog to the coll therdore rather than to the organim, and, in considering the material basis of heredity we are from to focus on the processes involved in the reproduction of stogle cell What olement within wan be ctpreted to carry hereditary in forgation? Consider the strator of a The basic structures of most cats are remarkably similar (Ftc. I) A cell i wrrounded by a coll wetsbrand and sometimes an outcr cell mal. Within tho membrane there is the Dock and cytoplam The mician of most cells is discreto body har ·- Choo Mochondo 17 Nudiu Macron Croplan Mentre Oturmane na tentation of ing a mudar membrane and containing thread like structures (chronno Home) Tho cytoplasm containg number of decreto element Mitochondria (mall particles having a defned and characteristic or phology) are found in profusion in the cytoples, and, by means of an clectron microscope, we can see soll salier particles (microtones) Thus the cytoplasm is found to contan different kinds of particolato elemeats, varying in sumber and u will be reco later in function, while In gedonal but a doglo oncleus is found per cell Tho cellular demonts that curry bereditary Information must be present in every reproductog call in addition, to account for the fact that klo fathfully bogets Hike, thero clements must be capable of reprodocng or dividing accurately The Ducien fulfills these requirements. For a ople, overy call capable of reproduction has a encleut cela lacking ODO cannot roproduce. Not overy coll has a well-defipod noxious, the bacteriu, for tramplo, bot oven they have characteristir at clear bodies. During cell dividon, the Eucles dtvkloa by an elaborato mochanten (mitos) that leads to the prodaction of cmct copy of aucb constituent chromosomno. It is the curomoromes to the midlows that cany tho material basis of beredity Chromosomes had been seen in nacid for a great many youn beforo thetr function was known. Tho proof that chromosome are bereditary olemonts came from the work of Thomas Hunt Morgan and his colleagues workdog with the frult fly Drosophila. To understand how it could be bown that chromosomes are tho bereditary elements, wo mit consider Lutofly tho aperiments of Gregor Mende Mandel, working with tho Cominon garden peu, found that certain churacteristics or traits appeared to bo fnherited todependeathy of one another For instance bo mated . trata that fared tall planh und bed wilallod red cont to ono that formed abort plot and had moothied coats. In the progeny the trut for talloe (o galart shortners) was transmitted in qual du ben to the plant that had wrinkled seed coats and to those with smooth rod couts. These observations led Meodd to conclude that to serual reproduc too the inhalace of one tralt is independent of the inheritance of est other Many ytan later honorer llorym and his associates, studying tho frult fly found that certain combination of toite ww framunthed mom ·The Matorial Basis of Heredity gother suggesting that the hereditary elements determining theso traits wers, to some way Inked Analysis of the inheritance of many trulta showed that they could be separated into several groups. Within anch group the train, and thacfore the heroditary elements controlling thern, were tnherited together Len they were linked. On the other hand, the Inheritance of trolls, each of which fell into a different group, showed tho Independence observed by Meddel. In Drosophila melanogaster four and only four linkage groupe could be found Cytological observations to voulod that the coll of Drosophile contalo procively four distinct pain of chromosomes. An loteresting coincidence. Morgen thereupon concluded that the chromosome mat bo the bereditary clements, and he was right. This can be proven by cytological study of the glant chromosoma present to the cells of the alivary glands in Drosophile. For oramplo a fly wus found to have an abnormal tralt, and that was reflocted in m abnormality in the structure of 000 of it chromo Fone. When this fly was mated to a normal fly and the progeny eumdood, It doveloped that every fly with the abnormal chromosomo had tho abnormal tralt. All the normal progeny bad tho Dormal chromosome. Thus tho combined use of cytology and genetic malysis led to the clear proof that the cercanosones of the nocleus carry the genetic material. Tho number of chromosomes per mucous is characteristio mod costant for each living organism. The somatic colls of higher plants and animals contain duplicato sets of chromosoma (diploid=9N) while tho gametle colle contain Anglo sot (haploid=N) Tbo gamothe cells of Drosophile have a chromosome number of the somatic cells havo & Tho haploid number for human calls is 23, for the fungu Nourospora crand 7 cod for the bacteriam E. coll 1 Theo bs a clour spodos specificity with respect to chromosome number and chromosome morphology Mitosts Shyco chromosomos carry tho bareditary toformation, we would ex poct them to be accurately raroduced and trosmitted in an adorly and preciso way They are. Sometimo during the Hfo history of the coll, an cact copy of ach chromosomo ba tynthorized When ooll division is trig gadd, a soquence of evento occurs which results in the formation of two call with identical sets of chromosomes. This typo of nuclear division is called mitosis. At fira glance, the nurlow stages of motors upport over whelmingly complicated, but what accomplished to dmplo. In brief the chromosomes contract and gather fodependently of Odo another on a plano approximately in the center of the cell Each chaomosome is then med to be dghtly paired with its previously yothetzed copy The sister strends, or chromatids, thon separate, one to och end of the call, and two Idental sets of chromosome vo formed. The Ducte reoponize, and tho cell divkes in two A mitotic cell divinor, then, is dmply division that ·17 Rp. 2 Photomuscrograph of atoms the watefish Who cu dron is ilggered the duplecod chromosome gather sad ppoer on distinct boothen Heuche The user Orromarom m Nepared od to color formed Copyright by Gwersi Kolegical Supply Hea hic Chcago ) produces two cele cach with a dential truckus. This is how to Fig 2 Mdous Both bapland und diploid calls an undergo mitosis in fact, mítosta is characteristio of deurly Jl celle Diplod colls, borror an undergo additooil typo of nuclear division, Delost which results in the radoc Hon to chromosomo bomber froca diploid to haplold. Such a division is obvtoonly Docentry who metto cells are formed from somatic cell.t. In mn, for bostance, DOT gection results from the furloo of sperm cell mod en og cell. The genetic cells were both formed by lodiriduab haylag #6 chromosome ad, upon fulos, must stvo nie to por todo ·Since botte cytological and genetic evidenco gino overwhelming proof that chromosomes CRITY the hereditary material, 4 study of the chamlal nature of chronovome might be apocted to gtvo insight into the chemical bar's of horedity Within recent years, It has been poplblo to iso- Lato chromosomes from the other cod stituents of the cell and thereby curry out chemical analyals of chromosomes. It turns out that chromokodas aro compleo, not only in terms of morphology but in chanlal terms us IL They do not consist of single chemical substance, but Rro compound, chlay of throo types of rubstances Protetus, dooryribonuclelo add (DNA) and ribonucleic acid (ANA) A brief word about these three subtaxes. They uro naturally occurring połymes. A połymet is a largo molocalo formed from a few stmplo molecules (the DNA mes ) repartody linked to chanical bondage Proteins are made up of vart- The Genetic ots combinations of twenty emplo mole cules-mino acids-and different pro- Material tetty may have anywhere from 100 to 10 000 units DNA and RNA are generally made by repeated linkage of four droplo units caled Docleotides. A DNA molo culo may beve us many u 30,000 units strung together the chemical differeaco between DNA and ANA, the signdBcanco of tho order in which the units are linked (primary structuro) and the total number of each unit per molecule (compor ton) will be discussed Later It is suffi dat for now to note that fruco puro chemical analysis of chromosomer, rouro .

·DNA The Gonetic Material pot able to conclude whether one of these thrco substances contains the goncti information, or whether tt is contained in Pombe combination. This As perhaps not too surpristog. Proof of this potot must come ultimately from btologlal tests. In order to establish that a certain substanco coatains genetlo toformation, pro Would Ice to isolato the sabstmce to pure form from 000 orgunkon and demonstrate that wben it is pot into another argudson, tralt of the first organiom appear in the second and ero perrod on to the progetry of the secood stimplo and sensitive test. To date, It has not boon postblo to do this with material obtained from chromosome of higher plants or animals, but it has been poonble to do precisely this with certain bacterde Trastorcatle Carlowly cough, the loes of inquiry that led to an understanding of the chemical nature of genetic material arose from a study of the portilent organko, Diplococcus pneumoniae which we paournomla During the 1920's, two bacteriologists carried out a kedles of experiments for which they showed that certain strum of the puoumococcus bacterium, when fnoculated into animals, would not aso syrnptoms of the disease. Sach trafns tro called avirulent If animals were tnoculated with a virulent train, the animal contracted poeumonia (Fig. 5) If olmak wero tooculated with colls of vtrulent train that previourly had been killed by trontment with beat, the animals abowed do symptoms. However when antal wero troculated with both rvirulent od boat Wed vtrobent cells, nalther alone sufficient for discuo production, symptoms of poetumoola did appour and, upon boletion of the organin glutng ibe to these symptommy, a vrulant strafp was found. Iforeover the strate retained fb viru lence through countlen cell diysloou. Tbo presence of heat-Lilled vtrulent colls, therefore, had the arlou efect of changing virulent ce li to vtru loot calls, which is chango to a genetic trait. This phenomecon wus called bacterial trafamation, and it study by Oswald Arary uod his collaborators at the Rockefella Institute opened the wry to the identian toa of the chemical nature of the genetlo material It h now hown that marry tnbedbed bectertal truit - undergo transformation, and that it can be carried out in a tort tubo o well to mice. For instance, again with the preumococcus organlan u ono ample, certain stratos are killed by the mtibiotic, streptoorycia (tod ato thus allod streptomycin-sensitivo) This knattlyfty is perred co from 000 call to another at all division. Other strains tre known to be resistant to streptoarrycin, abo a beritable trait. Suppose we perfam the following or podm-ot (sce Hiç ) Grow up a largo mas of streptowydd-rabtant bec terla Collect the bectaris, grtod them up unol all the cells are shattand, then mako a dlate Alt atrict of the man ud discard the insolublo coll detail Add come atract of the relatni strala to powłog population ·Howy AU PO H . Hudl tek Bectonal trandorition Wag na (na wtro) of sensition strata. Alany cells of the sensitive stran uro Don couverted to streptomycin-reabstant cells, cod they pets this resistance on to thetr progeny Extract of streptomycin-resistant cells, therefore, havo the effect of causing pamarcot hcreditary change from streptomycin sultivity to proptomycta resistance. It then proved poodble, by chemical fractionation, to bolate tho rabstenco th such extracts that causes this change to genetic traits. It was bow that the DNA present in such extracts to the active component. DRA mo cu Simple co Fig & lectorld trosfor nation to the test tube long, pied DNA nd the trait trup tomon me DNA hos Hence ch po ·DNA The Genehe Material 1 DNA at bo isolated from stroptomycin-redstant calls and highly purifiod. When this purlied DNA b added to the medium in which streptomycho- Kensitiro cells oro growing transformation of streptotryen-onstvo cell to streptomyoft-resistrat colls will occur This atraordinary phenomenon, Dolocular por if you will, may not captivate you from an orthotic point of vow but its importisce in tow of contubation to the understandtog of genetic material compot be overestimated Trimformation oun be domannstrated to otha bacteria Catan Atrains of fat rod allod Bacillus subtilis an grow the medium that does not contain the amboo add, tryptophan. Tryptophan tos Decennury for Hfe. It is one of the essential unit of Dearly all protein, od lfo as we know it camot adst without protetrs, Tho bacterium usoually obtaing its requtred ropply of tryptophan by synthestring it from other moloculos. This to called a tryptophetadopendent strain. There are other trains of Bacillus rubells that cannot make tryptophan md must have it supplied in their caytronment if they are to grow od divdo-tryptophao-dopeadat strains. Both properties, tryptophan depeodezco and tryptophan Indo pendence, aro berttable, DNA extracted and purliod from a tryptophao-todopeudent strain, when added to a growing culture of a dependent strate, will transform many of tho calls to tryptophan Indopendence. DNA thu folie the cuterla set forth cartier Lo., for a certato chemloul Aubatan.co to bo degmated us containing tho gobetto information of gtven organfoo, It abould be present to tho noclete a nuclear bodies and bould be able to bolato the pubstance od danonstruto that when It is pat into another orgmian, traits of the donating Orgunta appour to the second Netthar RNA por protein and activo to bectarlal transforma than. Tlous we may conclude that DNA is the chanlal rabotence which Xiva u tho buis of beredity Lactorld Viruses A second line of Inquiry that hu ako lod to Heatlication of the gooetic material u DNA # the study of bacterial viruses. For a better understanding of the nature of the evidence, It would be well to daalbo typial bacteatam md bacterial vtrus Becterla mo mitokopk, sngle-called organisms. They have char utaristic proclear the bodles (Duchcolds) which contain DNA. Bacterial cells ako cootuta largo motto of RNA, among other substimeen. Bo tatal vtrines aro still smalle but they am bo meto by moto of m dectron microscope (Fhg 8) Bacterial ytruses Dot reproduce to the absenco of living bacterial cells, and they are found to consist of only protet mod DNA The lo creo of typal bacterial ytrus (bacteriophage a fost plure) bgtved in Fig. The life cycle mary be dividod tato three distractie ·R7 Motorcrop porte He cote of Inter bodet. Corinary Dr C & labor phares the infective phase, the vegetative phase and the progeny formation phase The unfactive particle walch wus shown in Fig at Gaches to the bacterial cell wall by its tail A break in the cell wall o lodu od uod the conteots of the infecting partido and then lafoctod tato tho bocterial cell. This stop is of great Interest, became the bofectos per Ft Electron microgt plus of too dit went bacterial wont (Courtery DLW Lob!

·DAA MO CERA ODHA CA DAK CHINA 1 Hdo has a protein coat around a COTC consisting matnly of DNA. Thus the material that is infected into the buctarial coll and that tout Atts the formation of ny virus particles to DNA. After injection of the virus DNA, the bacterial cell goes into a period of vegetative virus forma ton durtag which de virus DNA and protein are synthesizod indde the bactenum. In the final stayo of this twenty-minuto life cycle, the Dewly synthesized viru protein and DNA .To assembled to new virus particles, the cell ruptures, and the viruses spill out into the medium. The padat of partladlar młerest here is the fuct that the material which is infected to to the bacterial cell, and which Initates the formation of new virus particles, t DNA. The genetic Information of bacterial vires thereforo contained in DNA Study of both bacterial trans formation and bacterial viruses contequenth leads to the conclu slon that DNA ta tho chentaal bests of heredity T Doudy o MD + Homepage -do Infective RNA whether or bestaba This conclusion however bring up a contemporery problema The Lf cycle of typ bestenal nrus of great importance. Dluny differ ther the native phone con cat vtries are, of course, Loow urt of Mechmend to the tatt te pt They aro Il extraordinarily anall rod ned for the formation In sto, and they all have m obli w phage prola w DNA Progeny how to mam t. gate requirement for a living host manbly phego DNA u pro for ropheation. In addition to bec ten nefecto particles terlal virur, plant and animal ytries aro well luxowi Whio bacterial viruses to found to consist of proteio and DNA, many plant and animal struges are born that condst of protein and RNA insted Tobacco mosake vines, a vell-known vtrus of tobacco plants, te of the latter type, as is the virus that causes 13 ·14 DNA. The Genetic Material human poliomyelitis. Uitng the tobacco mosaic viru (TMV) wo cm curry out tomo very fteresting aperiment. By conical means, it for poslble to soparate the protein and RNA copponents of TMV (Thoro om bo put back together to the test tube, wbere some stable viruses aro reformed thus at least some of the protein and RNA survive the sepert Hom nalofored.) If we inoculate a tobacco plant with just the protein fractlon, nothing happen. If, however fut the RNA component is troca lated, new TV partides are prodaced that have both the protein and to RNA components. The TMV RNA, therefore, carries all the informa Hon necessary for the synthesis of both the TULV protein and the RNA. In view of ach observations, how sure aro wo that, in higher organisms, the genetlo information is coded in the DNA of the chromosomes? Whilo Infectivo RNA is known in plant and animal viruses, we still know roletively little about the manner in which it replicates. Recent apert mental ovidence suggests that its replication involves in toteraction with tho DNA of the bort coll. The fact that DNA is the only pubstanco which, 1f transferred from ono cell to a second cell retalt hereditary changes to the rocood cell (transformation) L a strong indication that it is the primary robotance to which geetic information is coded. The trandation of genetic Information into action involve, B'wo will see, RNA. Tho tipo compounds are intmately relatod, and the very closeness of this relationship could well result to RNA abibiting an apparent primary genetic function under certain ctrcumstances, as to TV At the present time, therefore, it appemos reasonablo to conclude that in organisms, to general tho genetk tnformation ts coded in the DNA of Ho chromosomes, md that tho RNA Involved in the trumlation of the Information into action. For the moment, wo need not concein ourselves with the chemical structure of these compounds, for the structure will bo of greater interest after we consider how DNA transmits hereditary Information and how it can determino the characteristics of pocfc cells Armed with the knowledge that the matalal basis of heredity is DNA, let the riezt consider bow this substanco acts.

·Long before the discovery of DNA as the chembal beds of heredity the meritezen of well-defined characteristics in fosects and domestic plants bad beco studied by means of the basto tool of genetics, the battance test Tbo inbertenco tot COD- Hists of controlled meting od areful observation of the resulting progeny For cumple, two plants which differ to a given trult auch u color aromated (crossed) od the distribution of color in thetr offspring, od the descendants of thetr offspring is then malyzed This test to all o genetia, md was the experimental tool that coabled Vendel to formulate his law of inhattance Detalled study of the tranundalon of specific trelts reveals that they appear to be determined by specifc mon of a chromosome. The specifc area of a chrom mosome that determines spoclic trait Genes i be termed goze, Cepe odst in alternative forms (If thb ward not trike, and the inhaltance tort would be traposible) The alternative forms of a nogle gode kro Biochemical aled alelos. For example, one aspect of Reactions the property of blood clotting in manta determined by a specific region in one of his cloromosomat. The possession of this region in ope allolie form intura normal blood clottiog after plury On the other hand , arrier of an alternative form of this very cone chromosomal replon suf fer from dbeno bow us hemoplusu in which blood-dottlog Octans vry slowly if u al Certato gepes un bir to have many 100 different from And as we betoone more deti 15 ·16 Genes and Biochom col Reactions prylog, we will probably find that all gones entst in many alternate forms How then, are the gener wemblod? Through patient and careful study of the transmision of specife traits, individually and to combtraton, a concept of the genetic structure of a chromosome energed that can be likened to beads on a string. Each chromosome can be reprorontod ut a stoglo string of beads, with ach boud reprosenting a unit of gedetlo material, the gero Tho alloles of a given gone would correspond to difer ont forms or colors of a particular bead A perticular boud is present on only ono string at a time, and whatever the form or color of the bead (allole) It is always in the cemo place on the string. Nepropora Le Cycle To clarify and catend these Idows we will comidor fin somno dotall fnheritance in the fungus, Nourosport crawo Neurospora wa chosen bo mo it hus attracted the attention of a group of outstanding scientists wboso brillant caperiments with this organism have contributed much to our current understanding of the blochemical basis of gene action. Neurospora normally grow as a spreading mycolhim. The myceltum La composed of Individual strande, hypheo, which contain many pacle in A cotton cytoplasm. All the mudel have one not of chronowoTDOO, LO. thoy aro beplotd. (See Fig. 10) Vogotative or axial roproduction occurs by growth of tho hyphec and repeated poclear division. Asexual roproduotion also occun by formation of asexual sports called couldia. Noto ca 0 hich fr - Fig. 10. The life cycle of N roupon, ·Gena and Brochomical Reactions 1 particularly that the mature fungu ts haplold (as opposed to, my man wbob diplold) and that userual reproduction is based entirely a mitotic dividloos of haplold ruckel. Netrospon also undergoes strual reproduc ton Semal reproduction requires the fusion of two haplold nudd to give thee to a diplold nucleus which them undergoes a reduction division by mohora. Fordon of the two bepload buclel occurs through tho union of two strains of opposite mating type. These strains are indistinguobable, morphologically but they an be shown to diffa in mating type by tho fact that if strains of opposite meting type ut grown together characta Istke strual spores (etcospora) are formod. Strains of stmílar mating type, if grown together do not form soch spores. Tho tho matlag types are designated A od In sexual reproduc tlan, then, I cell will be formed contaming one haploid pucleus from strutn A ad opo haplok oucleus from straha & The modo fuso and gtvo diplold col. The fusion auxcleus then updergocs mesool in Lac-liko structure called am arut. Lots go over this carefully and give it your close attontton. You will fiod it rewardmg in understanding what follows Each racleus being to the scaval fusson an Identical set of cliromosode. Consider any gtven patr of chromosomes. In the fusion pudiem of the excus, they show strong mutual attraction and come to He very close to one another och gede on ono chromosome closely patred with 16 allele on the other chromosome. (Tho forces rasponudble for this pairing pro as yet unknown) At thus time, you will rocall, ach member of the pats appears a If It had split in two. As previously described, what is now essentially 4 chroTDOSOMES (tetred) undergo 2 reduction divisions and form 4 haploid rekel, the products of merons Each tetrad distributes Wolf todopeodently of any other tetnd, and hapłodd muclei are produced that can contain some chromosomes from one parat and some from the other Each of tho 4 products of melost then divides mitotically to gło 2 Adontal nocled, and the final result is 8 pucid that stero from the origtaal diplold nucleut. Sporo walls and formed round ach oncleus to form 8 Alcospore to the scoEach pair of sports represent product of net. ools, and the fndividuel ecosporos may be germinated to give rise to e Dow haploid, vegetativo organism. An interesttog aspect of Delosis fa Neurosport resides to the sac-like structure, the ascus Tho escues to our TUW enough to that in the divisions following the fint division of nelosis, the resultant noctel camot slip post ono another The roature ascus thus contetres 8 spores to bear unay and the ads of the ecospores reflects the order of their formation during metode The later tak. Test I. Neurospora Let us non consider the transmission of aspecto tralt in the orgm- La Neurospor Tally grows a spreading mycelium. A rarlant farin ·| Gones and Biochemical Rooctions is known which shows a button like or colonial type of growth. The colo nial typo con bo mated with a normal strain and the progeny eruntnod. Upon dicoction and germbution of the otght ascosporos resulting from sich a cross, four will show the colonial growth of the variant and four the normal sprouding growth. Hall of the progony are like no paroot, the other belf kto the second This would be cipected of the traft-spreading growth verrus ooloolal growth is determined by stnglo gone. The normal strut bus ngano (+) om one chromosomo that doterminer spread tog growth. The colonial etrafn hu an alternative form of this name geno (c) that reaults in colaolal growth. As hown in Fig. 11, the fusion nucleus formed by the mating of these two strelo contatos two homologoon chromosomes, one beartag the Ag. 11 The inherit c. of aglagere dfference Gore determiner tool type growth white He Moreal 1 la determine prodang growth The roquence of the loft data the udas beurrior Note that wegration occur + the ent dm wor, qoring ment in the wcu After loudle.) w ·Gmios and Biochemical Roochons 1 normal gero (+) and the record the colonial allelo (c) At melons, thero tro homologous chromosomes pals ind form a tetned. At the first dividoo, the replicated member of the pair are drive to opposite words of tho lain, md so segregato the (+) and (c) uloles from each other Tho rocood divisions spindles are then formed ad regregate the dater strods glytag two mudel having the (+) geo od two med having tho (c) gone. Each aucleus Dow mdergoes a mitotke division to giro four paded having the (+) goo md four mciet having the (c) gone. This emplo dauly Austrates the important general priodple that my truit in haplold organiem, such as Neurosport, which is contro Ded by a glo gene must show . ono-to-ono segregation to the progeny This toovitably fol low from the fact that there is equal genetic coatribution by each parent In tho formation of tho rygota, od that ach homologous chromosomo show equal replication Raidon Assortment The haplotd mucleus of Neurosport contains seven chromosomes. Spodilo goes are known to be canded on ouch of the coven chromosomer. This poses the question of how two groes, auch aurred on a reparato chromosoma, segregato durog melosti. We can answer the question by studying the transmission of two sets of traits, the truts botag determined by gends on different chromosomes For fastence urime that tho goro controlling spreading (+) vertus cotoolel (c) growth to bown to bo cutled on chromosomo No 1 In addition, maumo that a gre on chromosomo No. 1 doteronines the formation of anango cooldus (+) whillo in Delo of this gedo determines the formation of wilto or albino conldle (alb) Let us mulypo tho progeny that arise by coastog morango colo plal strata (+ c) by mn btno spreading strato (alb +) By camining largo number of spores solatod at random from many nach, we fod the followiog distnbution I per cent of the progony uro albino and spreading (alb +) e per cent are crenge, colonul (+ c) per cent and normal (+ +) and 25 per cent are albino colonial (alb o) However if we comto the individual spores from stoglo usd, we food that half the ard comted contaloed four albino spreading (alb +) and four orange colonial (+ c) while the other half sbow four Dormab (++) od four alhido colonia's (alb c) Lot to consider this pheromo- Don to tens of the behavior of chromosome Tho diploid cell or tygote formed by mattog colanlal ud an albido strun will contalo fonteen chromosomes consisting of seven poin. Chromosome I contributed by the colonial strain will carry tho gedo (c) Chromosomo 1 contributed by the albtoo strato will carry tho pormal Delo (+) of the same geda. Chromosome 2 contributed by the albino perent will auty tho also gove (alb) whillo chromosomo 2 contributed by the colonial #rafa will carry the Dotto aDelo (+) At meloks, botologou chromosomes pats to the repregate ·Gonds and Biochemical Reactions At tho fint metotic dtvilon, chromosome 1 of the elbino strun bus an equal chance of rogregatlog with its om chromosome 8 or with tho chromosomo 2 of the colonial strefn. If chromosomo I of the albino strun rogregates with its own chromosomo la ascus will be formed containing four albino (alb +) and four colonial (+ c) nucle. Lf, however coromosomo 1 of the albino strafn sogregates with chromosomo 2 of the colonal struto, recombinant nndal will be formed Half the model al curry both the normal geas of chromosomes 1 and 2 and half will cany both tho (c) and (alb) goes. This crumple Illustrates innafor prioriplo of genetics, namely that the usraatment of chromosomes during melods & nodom. Rendom Assortment, in turn, results in genetic recombination, Libed Genos Since many gones de carried on a dngle chromosome, wo must also condder tho transmksion of two genes both of which are curled on the sumo chromovido. Such gmes show the phonomenon of linkage, Lo, they uro tremmitted together more frequently than would be prodicted by chance. Such genes do, however undergo recombination un consoqueo.co of crossing over consider two gene patre, p/+ and +/= both of which are carried on the same chromosome, with a fertber from the centrovano thamp centromero P The contromnoro b the point on the chromosomo where the stater Ananda roman attached palar to separation, and it is abo tho point where tho Albant frcan tho splodlo attach and drew the strends to opposito poles. If tho strains (P +) and (+ 1) me munted, od progeny ascosporos Isolatod, the majority of the spores upon germination would bo of Odo or the other of the two parental types, oltber (p +) or (+ :) However recombinant strains to ako found, ie, strains that aro Dormal with ro spect to both truti (+ +) us voles the double mutant currying both the s and ptnult (p =) The two recombinant classes are invariably provenit in progeny in oqual proportion. The total mumber of recombinant progeny borrever in this case, is less than that predicted on a besis of random ar independent transmission. If these two geoes were transmitted todopend. ently of each other 2 per cent of tho progeny would bo liko noe parent (p. +) 25 per cent like the second (+ ) per cent would be pormal (++) . recombinant dan, md per cent would be the doublo mutrat (As) the secood recombinant class. Tho hallmark of linkage is the fact that the total number in the two recombinant classes is significantly less than 50 per cent of the progetry As shown to Fig. 12, recombinatioo of linked genes results from una change of segments between non-dste strands fo the coscły patred tetrod ·A (+ + Ft 12. Exhing beriman chromahok Note that magrogation accon after the second doradan romiting m 227 2 por rregut the foaned to the rypoto by homologou drooxosomes. The archange, temad Crossing Out occurs before the first reduction dybalan As can bo seen to tho figure, f break occurs between govo p ad exchange of the terminal segments will result to ono strud carrylog tho two pamal allotes (+ +) The other bomologous strand il aury the two mutant alleles

·Genot and Brochemical Rooctron
(40) Note carefully from the figure how the two meiotic divides then
rogrogeto the four different genotypes.
Whether or not e Crossover between linked genes has occurred co
bo readily determined to Neurorpora by Dotlog tho spore arrangement to
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don will result in their roparation, the ascus will show 144 anngement,
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·Gone and Practerico Rooction 2 over 1 CTOXover has occurred, segregation will not occur until tho pocond division, it will result in a 1.2 2. segregation, od the two parental and two recombinant dans will be present. This is dlagrammed to Fig. 13. In the photograph (Fig 14A) odo o cearly soo both cromover od pon- Tuborer u. NOT 0 Fy 14 (Top) Axl produced by the na rol of Neurosport ohrala that show heyed mation. Nota both foot and seconddri Hon egregatione (Cour y Dr Dorld R Stecher) (bottom) A schematic rop tentation of the gene map o of chrome one of Neuro por crowd. The number gome indicato de feront grant facting formation of the war he product the relativa de tance on the pan de Hred from combination dh ded the tet LLLLLLL 1 1 1 $ - - th ex re pestes egy ·Genot and Biochemical Rooctrons Tho farther way • gene is from the centromce, then, the grater the chance of a cromover between the gove and centromere, and the greater the chance of a 2 2 2 2 (second-dtybion) segregation. The frequency of Arst and second-division segregation thus permits the ordering (map ping) of gode relative to the centromag, for the genio dosest to the contromero will have the opallest ratio of 1st/2nd division segregation, while tho gero farthest away will have the highest. The fact that tho chanco of a crossover in any given part of a chromosome is about tho amo for any other part of the chromosome means that the farther apart two gopes are, the greater the probability that a crostover can occur Tho greater the probability that a crossover wil ocen the higher the fro quercy of recombination. Thus the frequency of recombination is a meus uro of the relativo distance between two genes. This fact permits tho proparation of gmotic mapa. A map of one chromosome of Nourospora is given to Fig. 14B For e dicundon of the details of the construction of such a mep consult Chapter 9 of the tort by Srb and Owen? Mitetton Geno configuration is not fired. As has beco mentioned, a given gono can edst in soveral different farms (allola) A chungo of a gene from one farm to another is alled mutation Mutation is of paramount fmportanco to the study of heredity for it must be ro-emphasized that we can be awo of the outstance of a gene only when more than one allole of that geno is observed. Tho raro putation that occurs spontaneoruly in nature provides variation and porndts the volution of now and novel forms. Ajutation frequency however can be increased experimentally This was fint shown by H. J Moller using X rays X-rays and other lonlang ndla tions incrouse mutation frequency aj do many other agents, ag, beat, ultraviolet light, and chemicals auch u nitrou add and nitrogen mustard (the mustard qu used in World War I) These and other mutagenic agents are atremely useful in genetic research, since they pant us to explore the possibilities for variation that are inherent in genetic na todal and to utilizo many mutant genes us tools in palmente Geots and Nutrition Wo to now the position to consider problem of primary comtemporary tutorat end research, tho mochanism of gone action. The gmetio tratts wo have discimed up to now have been mainly morpbologlal but we know that a blochemical bass must underllo all ench plo nomen. Call of a colonial form must differ from cells of a spronding form in blochanlal characteristia, even though the naturo of such differences 1 AJL Sib od D Oreo, Corner Comics (San Francisco Freeman, 1959) ·Gones and Blochemical Reaction I will unknown Such statement implies that gomo action ultimately must be preoble in terms of cell cbeindstry To get at the problem, wo obviously nood trufts that can be studied btochemically so called nutrktonal trato atlify this requlrosent. These were first fotenstrely studied In malcroorgelom, and here we got the first clour me. To grasp bor thato aperiment were wed for the analyers of gene action, borrever requtras some undartanding of cellular blocbanatry The besto cunctaristia of callole biochemistry pertinent to a discurlon of genetics will be binefly rovlowed here for a more dotatlod dascription, the reader is referred to the book by W D BicElroy in this Comparative blocheandstry has taught us that thero ore great sto llardties between calls of phylogonetically different organisms. A surpreng blochartaal unity , in fact, found throughout the living world. All living calls are studlar in comporttion md contain the camo classes of chemical compounds. Dorptto variation, all cells aro bullt from the ho building blocks, md all Hving things dood essentially the amo busic nutrients for growth. They requtro a tourco of carbon, a source of nitrogen, om alty FOTITC, and oturco of teruk. From these putrients, colls cyathod to their major chemical components such as protection, carbohydrates DNA, ANA, and lipidus well as the chemical compounds-such us amino acids and partno and pyrimidino beses-whilch corpore there on crocolecules. A coll syntheatres its vital component by 1 verlos of wol-defined chanical reactions. Most of these reactions require alorgy A coll, there foro, aurtes out another series of reactions in which energy can be trapped and forood foto tynthetic reactions. A content interplay this crits botween coergy roleustng and worry requiring roactions. The astonishing fact that tho ce can carry out all the necessary reactions mder conditions of constant temperaturo uod pravuro is due to the presence of specific catalysts, enzymes. (Remember to the laboratory tho chemiat can uso to operatures and pressures over many thousandfald hanges, wello tho human cell mux do Itn btochanistry at 37 C Add a proteiro of about 13 lb/in. ) Errymes, Hko other atalysts, aun markodly increase or do Couso the rates of rouctions without themselves undergoing chimgo. That to why only very well umount we needed per cell All enzymes are proteins, and many of them requiro a cofactor (vtta min) wully trall moleculo or a Dietelkon, to curry out their catalytro rolo. Emoo ne bo charactated by specificity Lo, a single onrymo can catalyzo caly a moglo rectken or des of Tauctions. La Fig 18 xentes of Horynthetic rouctions Illustrates these patate The unido argtalne, bo yathentzed from citruline, citruline to turn from ornithine ed ornithio from glutamic acid. Ghuttinto acid co bo medo from glucose by a loag .. مسلم دلدلما لم جہلملح للعملة D؟ NJ Prentice-Hal, Loc, 1991) ·COOH CK COOH COOH M <d C-O CEL મ 11 NH NH 1 CH COOH 1 CH CH HONH coor 1 CH du HOX booh C Habari coon Ale 16. The blochemical reaction required for the formation of me from qhucou The ruction in the OhVnion of ornithika to rn to rgin formation with the oder stop mon to the formation of the rubetence parios of reactions. This arginino is formed from glucoso by a large number of chemical reactions, and each of these reactions requires tho par Hepation of a poclic enzymo. A stullar series of events is found in the synthors of the amino acid, tryptophan, although different intermodiato compounds are involved. One last point should be Doted. While a mefority of the reactions involved in the formation of arginino ero common to the formation of many compounds, thero are a few terminal stops which aro unique. (Theo will be polotod out shortly ) This is generally true of the blorynthetic sequencos fuvolved in the formation of most cod products Living colles very considerably in thetr synthetto povrers depending om which curymes they possen. Obviously if e cel Outdot synthesto a certain sential compound, it requires that compound u a putrient. Therefore, dietary requtrements relact enzymathe capabilities. Somo o ganfoms aan synthesize all their unino acids, vitamins, and nucleotidos They got the energy to do this from relatively stmplo compotods like mugur Marry microorganbons are of this type. Plants, bowever are capablo of tynthestalog thet anno acids, etc, from oven smplor compounds, but thoy requlro sunlight on their energy Kurco. Other organitons lack tho nocessary enzyme to malo many of their carentia constituents, and so requtre them in their diet. Man, for instance, compot rynthostre his own vitunins, and can synthesizo only abont ono-third of has amino adds. Study of nutritional differences points to an important fact for the stody of goethos. Essen Hal compounds, liko amino acids and vitamins, aro rynthestzod by a soda of well-defined steps. An organbm can lose tho abill ity to synthestre such compounds and the low peed Dot prove futel, sioco thero substances am be provided in the diet. As a test, then, of whother or pot genes control cellular reactions, reactions involving the synthesis of ruch substances prove to be accellent peans of getting at the basis of the genetic control of cellular blochemistry For Carmpk, wlog an organlama ·Gonn and Biochemical Reactions which can synthesize all it Deeded amino ocids, we can determino whether a given mutation result to a putritional requirement for a gtven amino acid. If it does, does this ontritional requirement toduced by Imita Hoa result from the loss of ability to carry out a spodic blocheadical roaction? Experiments of this sort were taltated by the genetke, George W Bendo, and the blocherada, Edward L Tatum, for which they wero Iwodod the Nobel Prize in modscino tn 1959 Thar experiments with tho fungu Neurorpora crame give coactutive proof that mutation in realt In nutritional alteration, and that the best of the nutritional alteration rests on the loss of the orgonban a ability to curry out spodic Wochental reaction To voo tho basis of this conclusion, coosida o actual espatroont. Nourosporu utilizes pocoso as both a carbon and an orgy purco. It can utilizo nitrato antrogen xurce and requires ope vitamin-botto. Neurosport, therefore, grow on a medium cootutning puchoka, nitrito, blodin, and minerals (mintmal medium) Microcooldu (tho untaucleato bap- Lokd sporen of Naurorpore) cm bo treated with mutagen ach Xraya and there fordated spores can then be platod out on moriched minimal medlom, Le minimal modium to which the known vitamins and amtno aclds huevo bocn wilded. This mupplementation permits growth md survival of mutritional mutant. Under appropriate cooditions, thero spores Il grow Into dbcroto colonies. As a test of wbotha ar pot natation which Facts a nutritional trolt has occurred, en moculum from each colony cm bo pat fnto minimal medium. Under these conditions, some of the coloatos Te found to bo no longer capable of growlag ao mintonal medias although they are still capable of growing an arupplemeoted modtumn. These strutna pro found to require no Ribstanco to addition to the nooded matmal modfun. For instance, stratos are found which requtro urgtnine, othen tryptophan, and still others the vitamin, niacin. Treatment with a mutagenic agent on therefore lead to the formation of strutma hev tng altered putational characteristics Aro rach nutritional different beritable difference or are tboy duo to A Dangonetle or nonchromosomal chango? This question can be readily answered by Words of the Inhaltmc test. If marginro-requistog strato (4-) & crored with a parental strain (A+) the dght as corpores of anglo excus, representing the four products of mekank can be lolated and grown. When thout sporet oro gurmtrated on 1 medium containing or stome, all etght spores grox If these eight cultura de Dow transferred to i nedtum lachog arginine, four of the strats will grow cod four will not Half of the pas ve ugnino-dependent. This trait, therefore, regro gata u predicted for soglo toe differenco (refes back to Fig. 11 and in place of (c) substituto (A-)) This type of fnheritance is character lotto of all nutritional mutente Altation of a single groe can result to low of ability to form a spodbc essential compound.

·Gones and Biochemical Reaction Glass and Wochemical Reactions To pinpoint the blochanical nature of this induced nutritional alter ation, we must look at the cellular reaction tavolved in the formation of tho required and product. Let ou continue with urginho Tho blosyothiesta of argtntno requires the formation of glutamic acid from glucose. Ghibemde Acid in tim is converted to arginine through the formation of ornithino and citrulline, ronctions unique to the formation of erginine (See Fig 18.) Tho synthesis of argtnino actually tavolves the formation of compounds closely related to annithine and strulline, but, for the sake of clarity po will discuss its formation is described above. Mutent trains which itqutre arginino for growth can be tested for their ability to grow on thero compounds, compounds uniquely required for argtnine synthesis. a then i wil arginine-tequiring mutant grow on ornithtoo and dtrullide as well? (See Fig. 16.) We find that some of tho mutants will grow only when supplied with erginino. Others will grow on strul Hng, and still othan on citrulline or ornithine. Tboso mutants aro dot balochorically idential Odo clun appear to bo mablo to form arginine because of its ability to carry out the con version of otrullino to argintne. A second clea of mutants appears unablo to form arginino duo to an inability to carry out the conversion of ornithine to citrulline. They can, however form arginine from citrulling, onco thoy cm uso citrullino for growth. Tho third clasa lects the ability to form orginine, through inability to carry out the conversion of glutamlo sed to ornithino Each of theso mutants seeins unable to carry out ono specific biochemical reaction. This suggests that mutation of a splo gms lands to the log of the ability to carry out but one blocherical reaction. Theo quy > Gud COOH-C-c-6-coot + Or NH d-c-cod-coom + + Cm -- d-c-cad-coon All The gosti trol of the biochemacal recto con nth or gli fornition Cont pounds which a bowd for growth by the warlow stic de ated of the hott Alde + + NI G! M-C-N duc-cd-coon 1 ·Goner od Biochemico. Reochong If thero outents are crammed genetically vo find that all the strains that cannot convert dtrulline to argindino u genetically similar Al thera num rio by brutation of the same gene Similarly all the strains that annot convert onnithido to citrullino Involvo mutation of the same pong, but a gene destinct from the oce fust meatloved Shil a third pano ba food in which mutation results to the loss of ability to comvert glutamic add to ornithino. That appear to be clear Bsociation between a specific gone and the ability of the organlan to carry out e spocific biochemical rauction. This has fust been shown for argtntac. Similar remultu ere found for matians that affoct the formation of tryptophan, u well as for mutations that affect the formation of other vital mbatance Not only is thoro m isociation betwoon opo gero eod ooo blochemical reaction, but there to aloo spodicty a specißo gono controds pocilo blochemical rouction Struco each of the reactions tovalves nutymo atalys, tho 000-00o carrelation actually reflects a rolationship between genes and enzymes, rather than betroen genes and brochemical reaction. This currelation established by study of nutritional mutant is kdown u the 000-gene, ono-enzyme hypothesis and states that one gono control the formation of ano enzyme. The twer to ono question thru xhapo mnother How cm a geno control the formation of a spoclio en TYTO? To answer this, we must consider in greater detail the relationship between genes ad protem.

·. the previous chapter It w stated that apo ciflo genes control the famation of po cifio enzymes. This was based largely on tho obarton that mustatop of espedie geno may result in the loss of ability to any out a specific reaction. Additional ovidence mry bo obtained by testing for ODITY DOO activities to the test tube. Callfreo extract can be prepared both from a mutant straha and the parental strafn from which the matut wu dortved, mod tho eatricts criminod for the presence of the enzymo In general, melyrs of the atracts confirms that a mutation which results in the loss of ability to aury out a speclic reaction also results in loss of the eurytne activity that is requtrod for the atalysa of the reaction. The dear relationship between geno and certyme niggests that en under stoding of tho dature of thb relationubip mdght well go a long way toward explain- Genes ing bow goes act. Let us probo further It would be of interest to know for a and udple, whether the result of mutation is straply fallure to form enzyme or is a Enzymes consequence of a change in the structure of tho farmed enzyme Docs a goo stort control by regulating rate and other quantibiyo Sarantotto of ANTIDO formation, or does it control the architecturo of the enzyme, low the sequence of amino acids or their relativo proportions? For reasons of experimental expediency these questions have been studied in de tall only in microorgmhms, ad our discostom most deal with these organisms Howover It should be barpo ba mind that ·Gure and Enzyme 3 the principles daduced from the study of mkroorganisms ero genan ad porten to all living things, tocluding man, o will be documented for a cubuequent chapter Tryptoptas Synthetase A number of different genes and curymes have been closely analyzed during the past ten yon Sioco tho system wggest e stollar relattor ship of geno to CCTYTA, wo ato concentrate on coo well descobed system Tho anyme, tryptophan synthetase, has been studied to detail in fung and bacteria. This enyo ts required by these orgundams for the synthesis of the amino nodd, tryptophea. The formation of tryptophan turvalves the Synthesis of mobquo fatermediato, indoleglyceral phosphato (InCP to bort) Tho intermediate roucts with certo us shown in Fig 17 A mbathu Hon occurs between geride and the trtose phosphato portion of LnGP to stvo tryptophan and triace phosphate. This, the terminal step to tryptophan formation, is catalyzed by tryptophan synthetase (tase) Mutations affecting the formation of t uso com bo recognized by two criteria. (1) they are mutations włuch result in a mutritional requtrement for tryptophan, od (2) for growth, tryptophm amot bo roplaced by InCP or its procurtor mthrmlic acid. With Neurospora, a large number of conidiosporos ao be exposed to a mutagenic egont, e.g., nitrous actd, and wo can select out many independently arising mutant strains of tho abovo type None of these mutant strains hos mournablo tato activity to call-fron atracte. Such zu allelic srla con botsed to a number of waya to examine the nature of the getio-CDIymo relationship Ono poch problem ts In bow many roploos of the entire gmotlo structure (the gopomo) of Neurosport an mutation our and catate loss of taso activity? Is there a stnglo regiono oro there many rogloop This problem co bo opered by crosstag all the motut struins with ono other mod determining wbether tryptophan-bodependent progeny arbo. If there are two rou o reparto chromosomes, or two dbtinet trou om ono chromosome, both of which control tore formation, frequent tryptophe-independent progory will be observed a result of recombination when the tratts are crossed It, on the other hand, tho Teu to kentical or pay closely liked fow if my tryptophan-todepoodent 17 The reaction catalyzed by trystopise ratbatere, O. CHCOOH ہ + HO-04-C + 1 -96-OOM ·2 Gonor and Enzymes progany should bo found (ree Chapter 3) Crosses between members of the moutent les clearly establish the fact that they are all mutations of the pumo tree of the gezonde (Fig. 18) In Neunspor, this area is on the second linkage group. Tower A II. The chromatom of Noutoapon. It can be stated categorically then, that there to dnglo rogion to tho geoome which directs two formation, md in which mutation con occur to cause loss of ability to form functional enzyme Tho neat problems Does mutattoo in this gedette area docroutotho rate of formation of the curyme, or does mutation result in structural changes to the famod protein, or both? This problom can bo export mentally examined by determining whether as a consequence of muta thon, no enrymo to fornod, whether enzyme is slowly formed, or whether the altered gedo atill directs the formation of a spoclßc protein but one which lacks tho antalytic activity of taxe. To obtain ovidenco on the last point, wo must bo able to recogntzo and pinpoint a gtven enzymo by properties other than its catalytic activity This can be done by using for munochemical techniques Detectleg CRM It has been known for a grout many youn that animals can forin protons, callod antibodies, in response to a challenge by certain forelgo materials (antigen) For example, many of you have been fomnunized Agatost diphtheria md poliomyelitis. You react to the shots by synthests Ing antibodies which collect in the setum portion of your blood. If you then come into contact with other diphtherle todo or the pallo virus, an antigen-entíbody reaction takes place. The toata is neutralized and to dered harmless, while the virus is prevented from infocthug your nervo celk. Antibody formation can be dicited by many cubstances, trctuding ·Genes and Enzymos 33 prototns. Important to our discussion is the fact that mtigen-mubody reactions are highly specific. (Noło hor specificity is basic to sommy biological systems, antyes, antibodes, vinna ) Antibodies formed against ono protein will react only with that pootetua protots which ure #ructurally related. It b the specifctty of the entigco-antibody ro sponto that makes this a remarkably twofol tool to studytog the conto quences of oratation at tho cutymatic level Tools, of course, a protein and it can be purlied. If e preparation of purified tes btnfected foto rabbits, specific antibodies ure forded in response to a challengo by this mtigen. These robbodies aro present to thonblut scrum and can be recognted by the fact that seruin taken from the fourrunbrod rabbit completely inhabits atalytic activity when ckled to the enzyme whered serum taken from tho karby nabbt beforo tmmumtathan hus no effect on enzyme activity (Fig 19) Tho antibodies are Nord rabbit Irypto Heb Mom Trpprophan Me 1 Exynne mutral on t shbody podio for too tn that they aro without effect on other enzyme. Wo Dow have two ways to kleotify taco (1) by Its ability to atalyze IOCP + fortno - tryptophan, md (2) by its ability to react with taxo ant! bodlou. If these two characteristic roprosent two diffatut properties of tho proteta, wo hayo tool that pants the rocognition of the two proteta, oven in the absence of catalytic activity Tho potut of all this is that taso antibodies am be used to detect tho frarouco of protein which to structurally stollar to tuse, but lacks the ortalytic properties of taxe. To reet, ho want to know whether the matant too good aun no looget direct the formation of protein, ar whether It sul direct the synthests of a related but trymatically touc the protette. This can be atmoed as follossy (vec Fig. 20) A cell-freo Citruct of a mutant strain can be prepared a low enount of t so mti body is added to the atruct. If e proteto la present to the atruct which can react with these untibodies, t will do ro mod te them op. If some tako ·+ Antibody Tryptophan To + ontboden + To + 6 + rost Norrach free antibody Erayne Band 20. The tout for the pretence of tone of the parent or in proto which to related to the to addod, there will be no antibodies to Inhat the enzyme which can then go ahond and make tryptophan from InGP sering, and pyridorul phosphate. Suppose the coll freo atract does not contain protein which react with the antibodies. The antibodies will af course, rozdaln froc. They will neutralizo added ture and no tryptophan will be fortaed from InGP eto. Ultimately therefore, u Indicated to Fig. 21, the formation of tryptophan abows the presence of protein in the orlgtoel coll-froo atruct which can react with and remove tase antibodies. No tryptophan farme- Hon shows the lack of such a proteta tn tho extract Tase CRM If time-len mutand ero carmined to this way for the prezece of a proteta which is rerologically related to the parental enrymo, It is found that mutation may give rise to struins mabte to form a che protein. Such mutmt ero culled CAM- (CRI = cross-reacting material) However this is not true of all the mutant. The majority of the mutants do form • protein, und in normal amounts (CAM+) This protet will react with taso antibodies but is unable to catalyze the conversion of InGP to tryptophan. Thus mutattoo may result in loss of catalytic activity without rofiling a lot of aby to form a structurally similar proteto. This p8 gert that mutation, in this instance, is not stmply controlling the rate of aitymo formation Rathat it is effecttng enzymo structure. This fact can bo seen even more coovtoctogly in the following wey Tuo catalyzes the reaction InGP and scilne tryptophen (1) How over the came emtyme can catalyze two related reactions, indolo od perioot tryptophan (9) md InGP fodolo (3) Tho throo renc toos catalyzed by tese are shown in Fig. 21 Reactions 1 and 2 both require serino und pyrideaal phosphate, whilo reaction 3 bu no cofactor requtrements. If mutation alters TZYDO structure, we might predict that ·таю + HOCHCH-COOH M H HOT H-CHCOOH th + HO-CH-CH-COOH Tryptopher Rp 71 Th ructions catalytand by me mutations of the gene should be found which I roult in loss of catalytic activity to ado or more combbation of these reactions, but not to others, En bou of reaction 1 od 2 but not of 3, ar loss of reactions 1 od 3 but not of 2 If tho gene, bovrever to controllmg enzyme formation by control Ing tho nato of formation, wo woold predict that mutation in every auo should decrease all three reactions equally Mutations which result to loss of roucthang 1 and 2, but not of 3, TO found and easily detected, noce such strutas characteristically require tryptophan fat growth and accumulato Indole ta thetr culture mediuen, an ruch mutants aro CRA+ (le, react with tase anybodia) The CRM ou brolation and purification, can catalyzo reaction 3 m tho test tube. Shnilarly mutations which result in loss of reactions 1 and 3, but Dot of laro also found and again at endly detected, stoct rach stratos characteristically require tryptophan for growth, but they can grow equally well of grea trdoto tastend. Again, all such mutants aro CRM and thotr CRDI, on trolation and puriBeation, wil omtalyzo reaction 2 In altro Le, outside the cell Jutation which rerult in loss of reactions 2 od 3. but not of 1, havo not yet been observed, str.co rection 1 I the reaction Dormally involved to tryptophan formation )futations of this day would not require tryp. tophan for growth and would puss undetected. To pick up . mutant of thha khod, wo and freed with tho alarmtog prospect of maling catracts of thousands of pormal stratos to fiod ono mapable of carrying out 1 od 1 Similarly mutations which result ta loss of reaction 1, but not of 2 md Aro ako dincolt to detect. From such expertmental observation, we co conclude that cauta thong tin tho genetic region controllins l'are formation result in structural altations of the formed protein, rather than to quattatire atoutsoas roach o rute of enzyno formation Thib betog troe we must condado that tho geetle urca in koule may controls the structure of the formed enzyme ·+ H2O AMOM LY TH TH AN ALA CH LTH LALU Genes and Enzymes Protolas Tryptophan synthetuse, Hko all proteins, is besically a chain of unino actde. As previously statod, protetos oro composed of 20 amino acids to verying amounts, the amounts and their distribution lo the chalo betog o 1 1 HN-CH-C-OH + HyN-CH-C-OH o R o 1 H HN-CH-CTN-CH-C-OH Populda boed Hg. 22 (Right) The typical bond rtmg th meno od (BoHom) Temno od Loquence f bonne pancreatic bonuclara ARC ALA THE OL LYS HO m) MET MET CTS IAN CTS 10 sen OLY a ALA AP MH O AL MMO intimo LY LYS AN CYL TAPA ALA ALA LYS masa sau a ser AN Ma'a LYS ON AN CY son ELY TH own TITS (NA) } YAL CTD ALA LY! YAL AN ه مع ربعه ·Geros ond Enzyme = characteristic for a giren protein Tho amino acids to a protein are linked by coralent peptide bonds, and the anno add soqueo.co ts called the polmery stracture. The amino sold sequence of the chanc, nbonucleuse, which atalyzes the hydrolysis of RNA, I shoxo in Fig. 22 The busto or primary structure of all enzyme is made up in a fashion storilar to that of RNA. AN is a relatively mall malecale with a molecular weight 13633, while the molecular weight of tore is about 150,000. This difference, however simply means that whulo RNae ha composed of 194 mto add residures, tots composed of about 1,300. Detalled forestigation of proteos saggests that the acthie atalytic utes of menzyme coorst of only few amtso adds that is, the ate on tho Cuckymo rurface where IDCP combines consists of but a few of the 1.300 ahoo acted rekdoes. The fame is truo for the worldo dto. For cataly to occur a very spectilo orientation of these two attes with respect to exch other is required. To provide for this on enzyme moleculo does not anst o altreer atended structure Rather och enzyme bus a preciso folded structuro (Fig. 23) Experimental evidence tho present the piggests that the folding characteristics of protein may be determmed by the amino acid soquence. This conclusion may not withstand the test of time but, for the mako of struplicity we will assume that the unido actd se quauce doar determ to the entire thure-dimensional structure of inch Tymo. 2 My 7. Model of cole of the protesto qlobin The mode to besed ou to cretelegraphie data (Courtney Dr JC Kardin ---- ·Gones and Entymas En. Altstation Sloco mutations appear to result in alteration of cazymo structure and shaco enzymo structure to turn is determined by the amino add som quence, It follows that mutation must alter the amino add sequence of the product catymo. Can this be shown? The following discussion will mablo u to answer the question As mentioned earlier a number of difference can be readily do tocted among mutants which are all aliko tn roqutitig tryptophan for growth and in lacking an eryme catalytically active in converting InGP to tryptophan Some of the mutant are CAM- Other CRM+ Somo of the CRM's catalyze rosction 3 othan reaction 2, still other neither of the CRM's which aatalyze reaction 3, some require one cofactor others two, still others none. If wo cammino the CAM's carefully using quantita tive immunochenical techniques, we find differences botwcon them. If wo compare them to terms of the temperaturo that is optimal for their activity we find differencou. In fact, after careful stody outog mary diverso alterle of comparison, we are loft with the impression that fow truly identical aloles are found. Each allelo i functionally unique. This moans that the genetic area controlling the formation of this anzyme L mutationally complex. It does not consist of a singlo alto, alteration of which produces an Identical sot of mutants rather tho reglan mot conast of largo noonber of mutational altes alteration of each one of which cun produco a slightly different effect. As moreo tn Fig 24, we can mentally apand the genetio region aod rubdtvido it into many mutational sites This is what ODO would prodíct, if tho gero controls the amino acd sourenco and if each mutational sito wore to determino ane amino acid of the soquence. Mutation could result to alteration of tho sito in much a way that were the sito adginally to direct the faxertion of valioo into the sequence, it might kw replace it with lytino. This change in sequence would bo capocted to have an effect on the folding characteristics of the moleculo There would bo, is a CODsequenco of this one change a profound effect on tho activity of the product formed. And we would expect a large number of such mutatkou! eta, ed alt des yritton in structure. This is what is found. To rum up the geoetio ovidenco suggests that the gene controls the amino dd soquenco And that mutation results in alteration of sequence Mtoto 24 Nut trond viit the gene ·Genes and Enzyme What do we flod if we tackle the smo problem by proteta choo Atry? Can we by examining mutant protein, actually find amfao add Ribstitution? This is not mo try tmak The fact that on enzyme contains a total of soven) bundrod amto ucds of twenty different kinds makes the determination of untoo acid sequenco a particularly thorny problem. Tho Arst protetor whose entire sequenco was determined us torulin. In- Lotto contains fifty-omo unido selds, the final resolution of its requeDCO took moro than ten years, and the work led to a Nobel Prize for tho English bocbanist, F Sanger Fortunately catain short cuts now peruutt logoprinting of a protein These methods enabled Vacon Ingrata to demonstrate that there is Angle amino acid difference between two, geneticaly disthet, naturally occurring hemoglobins in nen Tho finger prtothog method an bo readily abown lo the case of RNase. Hagerprofiles The onzytoo trypato catalyzes the hydrolysis of certain peptide boods In protein, memely those in which one of the amino acids in the bond helther lystne ar argintne. This action ylekla proteta fraginents allod polypoptides. Troutineat of ANeso with trypsin wil break the moleculo toto Thumber of polypeptide. These can then be separated from each other by a method alled paper curomatography Tho rato of mgration on paper b chancteutic of arch fragment. If, for instance, two diffaent trypeln digests of RNuo of bovine origin cre chromatogruphed and tho two papan compared, vro And similor patterns of superimposable poly Peptido spot. If bowever a digest of bovtoo RNso is compared with thut of horro NNaso, the polypopuido spots are not puperimposable, in dicating that there are differences to the upipo scd composition of the fragments and thus difconces to the amino acid soquence of cow and horse PNase. Consider the Roquence nhakhty typ rol bord 10 11 12 Trypsta Trypce Treatment of this peptide with trypom will break it into threo fng ments, and, on chromatography To Hell find three decreto peptides However if the Na 9 glutamic acid is substituted with glyctoe, tho No 3 fragment will now occupy different podtion on the paper un couco qanco of it chongo to comportion If we compare the chromatographic prodles of these two, no And that the Na 3 peptide of the first propan Hon bu dileppered, and to have to placo a new fragment at differtat pot-on degent, yet simple method of showing amo actd dfarts.ces. A fingerprint comparison of votant eod porcoal too has bedo com ned out by Carlos Yonofsky futant CRAC's from E. coli havo bomo parlBed and subjected to fragmentation by trypsin. The peptido in groente have then been reported from each other by appropriate chromatog 8 . 7 8 ·0 Gonos and Enzymes naphy Chromatograns of the parental tase and prepared in exactly tho umo wry md the two Angerprints compared. Some mutent CRM uro found to have fingerprints idential with that of the parental entyme. Moro important, however is the fact that several mutants havo been found whoro fingerprint differ In orch Instance, the difference is found to tovolvo only ono fruguvent, Lo, the absence of 000 purontal fragment, with the opporrence of a Do Donparental fragment The fragment tovolved is charactedstic of the mutant, abowlog that the change in the wino acid Loqueoco differs to mutents of todopendent origin. The fact that a peptido difference is found means that tho mutant CAM diffans from the parental enzyme tu amino add composition, although the cunct diffcrc.co bas still to be determined. A word of cautionthe fact that CRM's are found which show no fingerprint difference to not Doceserlly proof that bo chemical differenco exist. It amply points out that the difference to these cases may not be detectablo by present methods, for the present methods will only dotoct alterations which realt ti difference la cloctric charge or in chromatographic properties. Thus substitution of glutamic aad (a dicarboxylic add with e nogativo chargo) by lyst (u diamino acid with a positive chargo) can be detectod, whillo a substitution of loucide by vulino (both uncharged) could pot bo detected. At present, therefore, cases in which differences can be dotactod are per heps moto meaningful than ausa showing no difference. Howrova wo do know that mutation at the tryptophan synthetase locus results in cases of donnonstrable fingerprint diffaences, and wo an stato with certainty that mutation of this geno results in structural alteration of tho formed cultymo becuse of difforonces in amino add roqueace. In addition, no koow from work with other proteins that mutation at a single mutatlooal sito appear to Totalt in the alteration of but Odo amto add In summary all the present expertmental evidenco clearly indicates that tho godetlo region controlling the formation of tryptophan synthetas controls the structural characteristics of this entyme, Le, the primary antoo acid roquace. It is true for this enzyme, and study of other genes and other optyma loads to a similar coacheslom. Ono function of godotic material, therefore, lavolves the determination of enzymo structure. As will be discuted later this conclusion does not farce the further coclusion that all genetic material must act to the same way Other genetic ureus do play a role in the quantitative regulation of anytho formation, but most enzyma probably have a gene that acts by controlling structure, and this action of gecette material should thus be explored further It to dow apparent thet e geo which controls the structure of 10 enzymo must be able in some way to serve as an amino add codo. Lo addition, # must bo able to trrostalt this code to emtymo-formłog coton. Since the chemical basis of beredity appears to reside in the compound DNA, wo book to tho properties and characteristics of DNA for hints to the solution of these new problems.

·Researchers have found that DNA co bo to lated from cells of Deaty all living organ- Isme, ud, indepeodent of the contre a11 DVA I found to have many of the same chennal and pbysical properties. We no longer doubt that DVA 1 vital coch pooent of tho chemical beb of barodity HoweveToba DVA alone contains all tho sedetle toformation, or wbothct DNA must act no concuit with other de torte, protein for ovenpic, is not a known Fmal resolution of this problema must come from crperiment. To date, no experimental tochniques have been do visod that pamit the completo purißen Hon and blologlal testing of DNA. Dloroover Do DNA synthesized to the labor tory has abown cay Dournablo bologia! activity Afore about this later The reseination to bear to miod, then, is that DNA, while the major Tpanet of genetic material, may not bo the only component Genes in Action The Structure of DNA DNA & macromolecule of vulablo polocular weight. In general, It is com porod of four repeating units called orucleotida Tho pucleotidos uro fully complanted molecules theolves. The ad coobain pbocpboak add mod the Scarbon rugo dcorynbasa Vero they differ is In ther third cacopoeat, the buse. There aro four bus most frequently foand tn DVA, two purtnes (dealne, gIDO) and to pyrimidines (cytotec, thymine) Toolidual berer in contano 41 ·2 Genes in Action Hon with decyriboso and phosphoric acid gtvo four nucleotides tho puroo mucleotides, dooryadenylio and doorygumike adds, and tho pyrinddino mclootides, deatythymidilic and dourycytidytic acids The chemical structures of phosphorto add, dooxyribose the bases, and ono purlpo nocleotide are given in Fig. 5. Included in the figure is the bond that Hobo o unit in the chain with another This is a phosphoester bood which Ibbos tho deoxyrlboro (carbon 3) of one bucleotide to the deoxyrlboro (carbon 5) of its naghbor Tho DNA chain is made up of a dooxyribore phosphato backbone with the buses ponting forward and papendicular to the Aber od. A number of years ago, Irwta Chirgaff and his colaboraton a tractod DNA from a variety of sources mod measured the relativo propor tions of the four aucleotides to the połymer La, the beso composition, Some Interesting results turned up with any gtor nucleotidla (tato adcoino) the relative amount of the unit to the DNA frono, my animal, froroct, plent, fumgal, and bacterial cells, ruded tremendously However tho utonishing thing was that with any gloen DVA, if all the poorino nuclootides were added up and all tho pyrimidine nocleotidas added up, the two pwms wat oqual In addition, it was noted that the manber of F. 26. The reporting unt f DNA NY NH OM COOH 1 1 c- Ding HO TY OH 0 OH - H o H 00 OHH M or OH H ·Gurts un Action 43 dooryadenyle add molecules wu always equal to the number of do Grythymddylio add molecules. Stullarly deoryguanylio add w equal to deoxycytidylic acid. The following to in utichal bat Ilustrativo amplo Doorthymidyl Decreertichato Dearredemptio Decagemength ad ald ald ( And of coper any) 10 40 10 50 20 80 DVA DVA 10 10 The Watson-crick Model Thero observations, together with stodles of X-ray diffraction pat tarta by M.H.F Wildas, led Jame Watson and Fructs Crick to propose a structure for DNA which to shown to Fig. 28. Watson and Crick suggested that each moleculo of DNA U zoede mp of toro Intertwined strands, and that the sequence of baser in Mo Anind determines the so quence of the other the complementary strand, u a AD consequence of pening through hydrogen borxhing CE between tho pudno od pyrtonkino bure. Wherever dentro occurs to one straod, pelring to the compla mentary strund is with thymfpe guanino ba paired with cytostno The outstanding characteristic of the proposed structure of DNA b that it is dooblo strcoded and that the two strande no carpzpentary Extendre pbylo and chemical investigation support the doublostruded picture of DNA, and our thoodles on the modo 26 Schwests de gram of the W tron-Cold model ONA The pearing of the best by hydrogen bandera indicated o NE o -------- 0, ·Gani in Action of repliation and mechanton of gene action mut now include this fact Repikatlon Wo know that the gerette material of a given cell must be able to replicato itself canctly The double-stranded nature of DNA provides i attractivo hypotheats for the mechanten by which genetic material dort blos. Assuno that, at replation, the two strand of a moleculo of DNA soparite, and ench single strand maintains its structural bategrity Baro pairing between edenine and thymine und between guanino and cytosino then tmplies that each soglo strand can force the synthesis of an image of itzalf in the couplesmentary grand Talo & molecule of DNA and label tho atrunds I and II. Normally I and II form a tight couple At roplice thon, I kod II separate. Strand I directs the synthesis of a Dow II similarly II directs the formation of another I The result is two molecules of DNA that are identical with the first. Such a method of replication would pornit preservation of identity from generation to generation, for a strand onco forined would remain intact and would dictato the structure of it nowly formed complementary strand. In addition, if the base sequenco were to serve as the bereditary code, we have a way to prove and tranmitt the codo. The question now , what evidence is there that replication in tho coll fuvolves a process of strand separation and directed ryothesis of complementary strands, with cech original strand renaining intactP A number of acting crperiments have recently been carried out to enamtno theno polnts. A series of studies by Alatthew Metelson and Frank Stahl will bo described at length to the trato one kind of esperimental attack now being made. If you look at table of atomic weights, you will seo that nitrogen has an atomic weight close to 14. Most nitrogen atoms do have this weight, but there is a stablo (Donradioactivo) botopo of nitrogen with an additional neutron in its nucles and an atomic weight of 15. The is heavy nitrogen, N Bacterial calls will grow in a medium containing eltber normal bitrate, NO, - or heavy nitrate, N''0,- If the nitrate toa b the goly source of pitrogen for the bactarium, the oltrogen atom from NO,- will go into a) the molecules that have nitrogen pert of the structura fn particular the buses of DNA. DNA, atracted from bacteria grown in NO, will have a higher density weight per unit volurno than DNA from bacteria grown in N O - This difference in dewrity makes it poroblo to separato houry DNA from ordinary DNA in the centrifuge. Unde standard conditions, movement of a moleculo to a centrifugal Beld (vedimentation) depends on its denstty Heavy DNA, with nearly all of Hos otrogen a Ni will have a higher sedimentatton nato and moro a greater distance beforo comfog to rest (equilibrium sedimentation = S.)

·Gones n Action than will ordinary DNA, A DNA molecule with balf Nu and half N44 will hevo o S.foxt in betwocn the other Mesebon und his associato grow cells of the bacterium, Escherichia coll, in N", for many generations until virtually all of tho DVA com tafood NW (DNA") Tho calls prad harvested put into a medium with only N140,* and grown for just that kaugth of time requtrod for ach coll to atrido once. The total number of cells bad now donbled, the total amount of DNA bed doubled, and much moleculo of DNA had donblad The total amount of DNA must equul tho total amount of normal DNA. A emplo of the cell was then taken, the DNA extracted, and S.meutuod. It fall just between that of DNA" and somal DNA Let us consider tho prodiction of our original hypothesis on the mocłuntans of DNA replication, od the prodhonthou dertved from a contradictory hypothods. The original hypothesis w If we tart with a cell having DNA both streda aro beavy and wo buvo strwch I and II" Lot this DNA" roplicate in N0,- medium. Each strand rombos Intact. The complementary strmod cynthetzed by Its them IT and that of II" E T Tho call divides. One cell gets I 'TI DNA, the other l' IT" DNA. Tho DNA molecules are fdential, och hos half of its nitrogen - Ns the other half - N od the S. of this hybrid DNA should be between DNA" md pormal DNA. A contradictury hypothesis is DNA strands do not romain tobact. Thoy soporte, break down, od the pot strands are formed at random from tho Nu beses contributed by the colgtral DNA and the Dow Ni beres made by the cells from the N40, in tho medium True strand I malowa now II und strand II now I, but now the NU in auch DNA moleculo o distobated equally between the struds, od we wlod up with two DNA moleculs, IT, KI II u X Remember that before, on rund in the DNA moleculo had all the Nuto III The two types of DNA pre ticted by the two hypothesa aumot bo distinguished by S, octement Noto carefully that while the predicted distribution of Nu is sharply different, both types of molecula bavo the mudo danber of Nu stoors, mod it to the number not the distribution, that detamboes S. Howover let the bacterial collo go through fast one moro divodoo ba N'O - Now the predictloos lead to divergent consequaces that are caperimentally mouunablo. According to the recood bypothest, agata the DVA break down. Since anch stred ho bat one-half of its original N when it form & DC Irod, each per stradd wl best one-quarter of the odgml N Biaro Important, coery strand wol buvo about the smo imount of N Consider the consequake of tho orkutoal hypothetts. After ono distson, I and IT were formed r IIM tn N10,- will now sepurato mod farm land IT r I Instead of all the strands being uke, and having ove-quarter of the original N r have two different species of ·46 Gonor in Action DNA, oo with all Ni normal DNA, the other speda still with Ono-balf its original Nº If they odst, they can be separated. The parlmental result wu that two spodles of DNA did ait, not mo. Moreovor the houvy spedes contained wo-half the original Nu content, not ano quorter Thba ts 1 boxutiful apartment, brilliantly conceived and crecutod. If you buvo mastered the concepts, you have a taste of tho Hod of work gotng on today in molecular biology Of course the aperiment does not provido a Anal onsyror It is consistent with, and affas support for our origtnal hypothesla. It disproves the second hypothesda, but tharo oro other possibilities. Why not think omo up, and so if you can plan on esperiment to tost it? (Suppose DNA Dot two-ttranded, suppose it is forraddod?) There is ovidcoce, then, which points to sencorvatve method of DNA replication in otoo in the living coll, that ts, the physcal integrity of a strand once formed i preserved Experiments in higher plants also load to much the sumo concludon, Ono puch clover cyperiment by J Horbert Taylor makes 1000 of thymklino (thymidyllc acid without the pbospheto add group) Some of the hydrogen atoma of thymidine ure replaced by tritium, wbich ba hydrogen atom with two additional poutrons to the ruclou. Tritium is radioactive and can tako its own photograph when aposed to certain types of Alm. If root tpe of the bean Vida faba aro grown to tho presoco of radioactivo thy midtoe tho thyrnidino is incorporated into DNA u doorythymidylto add ind uso to be distributed throughout all tho chromosomes If the chromosomes are now permitted to divido once in the abortico of ndiouctive label, wo now 500 One strand which is labeled with redioactivity and ope unlebelod strand The lovel of organization at which these observations aro mudo bs at the chromosomal, not the moleculer lovel But the observa tions again point to the conclusion that there is a base doubleness to the replicating genetic structure, be it e viablo chromosome u wo find to Vicia faba or the DNA molecules to find in bacteria. Additional wyportlog evidence for the proposed method of DNA replication comes from crymatic studion carried out by Arthur Kornberg und his collaborators Theso workers have shown that DNA, os character ized by its physical and chemkal properties, ceo be synthesized th otiro Tbo conditions of synthesis require not only the presenco of the muchos Ados, an energy sourct, and a specific antymo to atalyze the polymetla Hon, but abo i mall amount of speclic staglo-struded DNA (doublestradod aun ako be tied but is not as effective) to serve na prima or Initiator (perteps model would be appropriate) for the reaction. Tho DNA formed to the mouction be the physico-chenlaal properties tocludtog base composition of the primer However biological activity of the source of the prime DNA EU Dot been duplicated. It would be very oleo to take troforming DNA from the pneumococcus, make It pogle- ·Ganes Acton 1 stranded (you can do this by beating the prified DNA, which seiva to operate the strunds, and then quickly coolbog it to proveot the strands from roussodatog) and make more tramformng DNA in tho test tube. These crpalments havo Dot yet succeeded, but they are golog on and there are great expectatiam All the contemporary apatmental ovldon.co potnt to the conclusion, therefore, that genetlo material is a double-stranded structure and that this structuro ropliantes to a semiconservativo may Le by separation of the two arunck, with each stoglo strud mantatotog physical integrity during roplication Whilo dodies on the chemical structure, synthesis and mechanism of roplication of DNA are going on other peoplo ere wocytog about another problem, tho problem of the structure of gone information Ceno control the roquence of wratno acids in Outyme (od probably to all protets) A part, perhaps all of the gene i DNA. Therefore, DNA controls the sequence of amino ads in enzyma DNA combts of four beves. Protetos conabat of twenty amino acids Hon cm DNA bo coded so that its genetic information can bo road off us an emino acid moquenco? This is a fold in which thero ao ko few facts to work with that speculation is abea dallght. Cryptography Again, the cryptogriphic problem is to work out a four-letter code (the nucleotides) to gtvo a dictionary containing 20 words (the amino cids) Many woluboos ero poudble, and the will describe one rostulttug primarily from the analyse of Skoey Bronder md Frucis Chick For oto of discusson, let the mucleotides be the letton A, B CD As far is known, thero ero no restrictions on baso requenco in DNA, WO have, therefore, u many repetitions of euch letter as we pleuke, od they can bo grunged in my order for enemplo, ADCCCCBALADB ODO letter to obviously not enough to spodify one amfoo add, for that trould tako curo of only 4 of the 20 unido aade. A two letter wordt also fomuident. The fint lottar om bo etha A, B C D That gives four pos dullitha Tho rocaod letter of tho word can also be alther A, B C or D This gives 4 X 4 = 16 different words (A4, BC BD DB ad ugain this filh sbort. Wo try thrco-letter word. The first letter an bo other A B C D u can the second and the third (e., ABC BCA, BDC CDB AAA ) This gtves 4 X 4 X 4 = 61 possible words to spocity 20 unido acids, m embarrassment of Hehes. Some re strictimu must bo placed on which of the words malo senso and which uro nonstose, to prevent tho amino acids from becoming confised. Another powblo source of confulon must be considered with refer mco to the form of the code. That do we wmt an overlapping codo or ·46 Genus in Action DNA, with all N4 normal DNA, the other species still with ooo half Its origtoral Nº If they arist, they can bo soparatod. Tho experimontal gorult wus that two spocte of DNA did edist, pot ano, Morcover the houvy spedes contained one half the original Nil content, not ono quarter This to a beautiful palmont, broliantly conceived and arocutod. If you havo mastered the concepts you have a tuto of tho kind of work golng on today in moleculer btology Of course, the experiment does not provido a Anal mower It is constent with, and offer support for our Origtoal hypothesis. It disproves the socood hypothesis but there are other possibilities. Why not think oo op, od see if you com plan en experiment to test it? (Sapporo DNA is not two-stranded, suppose It is four-trended?) Tharo ts ovidence then, which points to a semiconservative method of DNA roplicabon In otoo in the living cel that is tho physical integrity of a strand onco formed is preserved. Espartments in higher plants ako load to much the same condodon Opo such clover experiment by ) Herbert Taylor makes use of thymidino (thymidyllc add without the phosphato acid group) Sone of tho hydroto atoms of thymidine are replaced by trftlum, wbich is a hydrogen atom with two additional neutrons in the nucleus Trithurn is radioactive and can tako its own photograph when exposed to certain types of Alm. If root Hps of the bean Vicia faba oro grown in tho presence of radioactivo thy midine, the thyraldine b Incorporated into DNA us dooxythymidylic add und 1 seen to be distributed throughout all the chromosomes. If tho chromosomes are now permitted to divido onco in the absence of a redioactivo label, wo Dow see one strand which is labeled with modtoactivity and ono unlabeled strand The level of organization at which these observations To made to it tho chromosomal, pot thomolecular level But the obrevi Bioms gain point to the conclusion that there is a base doubleness to the replanting genetic structure, be it a visiblo chromosomo u we find in Vicia faba or the DNA molecules we find in bacteria Additional supporting ovidenco for the proposed method of DNA replication comes from onzymatic studies carried out by Arthur Kornborg od his collaborators These workers have shown thet DNA, o character tred by 10 phytal and chemical properties, quo be synthestood to oltro The conditions of synthesis requtro not only the presence of tho pudeo- Hides, m energy source, and specific chrymo to catalyze the polymerize too, but ako moell amount of specific single-stranded DNA (doublestranded an ako bo trsed but is not as effective) to serve u a primer a inltlabor (pesteps model would be appropriate) for the reaction The D formed to the reaction has the physico-cherddal properties including baso composition of the primer However blologlal activity of the sourco of tho polme DNA has not been duplated. It would be very nice to pake transforming DVA from the ppeumococcus make it sloglo ·Genes Acton OH CH CH 01 CH POL It to clour that he would like to have mutagens reagents that will cuso baso substitution Ioatzing radiations such us X-rays, are highly mutegenk. Tho effects, In part, aro chromosoma md me due to deletion, toverdons, and trans locations, the latter two being restringements of chrotoromal material Thoso occur bocars X-ray can break chromosode, some places an bo lost, while others om recombine but in diffamt order Ynys also probably Carlso beso abstitution, but this a potot that is diffcult to provo Ultraviolet Hght k also highly mutagenic. Liko X-rayz, ultraviolet ndha thon can give note to both chromosomal alterations od point mutatlon Again, tho moleculo hands of the action of trestolet Hght is not courty hown. In rocent years, another class of mutagens has appeared and has been found to be of great interest m connection with bavo rubstitution and mutation. This is the class of chemical matagens, one of which to the common fnorgank acid, nttrot dd (HNO.) HNO, b a potent ouldızing yent. It a react with potimary amino groups, such us aro present to the bases, and replace the amino group with an orygon atom (F1g. 27) As shown to the Agure, the reaction of ANO, mth cytosine yrelds uraal HNO, can also react with adealno od convett to a different bus, Ctheme hypornthine, Supporo HNO, doo roact with cytosino m DNA mole calo and convert it to uradil. The Ouldette dermination of cytown by strand carrying undl, opon replian tion, o'ght Dow mako 1 mistike to patring, and, rather than patr with guanine, patr with adente. In mbsequent repletion, adentoe, to turn, will pair with thymine. HNO, will thereby have effected the transition of a gumino-cytonino patr to on edenine-thymino pa'r thus altertog the base requence of the DNA Nitrow add was first shown to be mutagenic to tobacco moslo vtrue. It to now known to bo mutagendo for bacteria, bacterial virures, cod fugl, and it appears likely that it is mutagenlo to higher plant o well Nitrous actd, homover does not offer the spectietty that one might le, for # Dreast to the embro goup the three boxes, edenlos gustos, and cytostne. A technique which, to the long rum, may prove of greater value to me tavolving some trickery Blake i compound that looks liko ono of the buses, but bose belastor a bit diffamt Such compound might hoortuink the cell into incorporating it into D, ead, once in, it might foduce pelring mistakes. These comporrods are alled buko ma Logom. Ono compound of this class is b-bromondl It La locoported into the DVA of bacterial viroses normally this bate - pair with HO- Uh. Ft 27 ifrou cd ·2 Gonos in Action denine, u does thymine. From structural consideration, it is conjectured that B-bromoured should alto pair with guante The presence of 5 bromouracil in DNA thereby might chance the likelihood of transitions of the type guanine/cytostne to odenine/thymine. It is pleasant to report that 5-brosound is fomd to be highly mutagenic. A second bare Lalogue, 2-aminopurtne, to also mutagende. Liko 5-bromourel, it to Incorporated into DNA and in this are appears to create truositions of the type odolno-thymide to gumine-cytosine. It is pahepa interesting to poto that amino acid malogues are not mutagento fact which permits confidence in tho base analogue rosults. A curious addo in connection with 2-aminopurtuse ho to do with tho phenomenon of mutator genes. Genes have long boem bown which, when putzent to the geporne, enhanco mutation rates of other gener fr the oryanlım It has recently been observed that a mutator gene present in a struth of the bectertum Salmonella typhimurlum has the effect of causing tho orgmbm to produce 2-oninopurine, a bruilt-in mutagenic Agent Ertenstve investigations by Erost Freeso and Seymour Bentet using bere analogues, gtvo strung support to the notion that substitution of ono baso can causo a mutation In the yean ahead, with the acquisition of still better reagent, it may be possible to ortend studies of mutation to the molecular level, for it should be possiblo to obtain reagent which will substituto only for adentre, other reagent spedfic for thymido, and others for gumino und cytostae Certamly thds is one of the promising approaches avallable. There is ono final question to be considered to this chapter Supporo DNA docs determine the amboo acid sequence of protein and suppose wo do have the correct codo How then, is the information transmitted? Mossoger RNA Here again, tho evidenco is fragmentary If it weto certain that protein synthesis Octunt solely in tho nucleus, it might be mspectod that DVA serves directly as a templato (pattern or model) and that the chromosomes were the actual sites of protein formation. Expertinental evt dence houtver has revealed that protein formation occun mainly to the cytoplasm, in specßc particulate elements alled microsorder. There foro, we must conclude that m intermediato substance operates between tho gene and the proteto whose formation the geno controls. The suspect Lottribedlato by RNA. Tho second major polynucleotide of living matter ANA, exists to all cells. ANA differs from DNA to its best composition and its pontos, tho 8 carbon sugar component. The beses no dealne, guanine, od cytostoc us in DNA, but with uradil in place of thymie Its pontose lo ribose nther then derevribose It has been known for many years that RNA present ·Gores i Action ta tho cytoplom as well as in the nucleus end an impressivo amount of data hes born obained that tmplate RNA in the formation of proteins Studies on the synthesis of protein in altro furtba suggest that a number of different RNAIre requtrod u bocerary cofactor for protein Sydthost For detailed discussion of protein synthetus, the reader b referred to the book by WD AcElroy to this setia At thb paint, wo will not concer ourselves with the diverty of RNA,, such as the imino ecfductivatiog RNA, tho mícrosomal RNA, etc. but solely with the relationship of ANA and the mucler Ono solution to the problem at hod would be for the DV of the nucleus to direct the synthest of an RNA. Tht RNA would reflect the specificity of the DVA and would then setVO us a messenger In fact, it be referred to as mes Hon ger ANA. It would migrato from the modew to the cytoplasm and by tnteraction with the DIKTOOTDE, KNOW a specific curyme forming ate. Tho cedibility of such a proposel obrtowly depends on whether RNA syntha's oorun solely to the nucleu, Epperlments afroed at - wartog this question poggest that this may be the care In Neurospon, for Instance, ma como experiments curied out by Varto Zalokar do cytoplasmie ANA syntheats was obectved. RNA wu formed in the nucleon, and ovklenco mu obtened that this muclear RNA migrated out to the micro- Order. These observations support the theory that an RNA surves as a merrenger botween a gede ud tho te of formation of a specific enzyme. Additional sopport for this idea COTDe from current studies of bacteria and bacterial virures and from the fact that RNA synthesis ppoars to Occm along the chromosomo streads. Usturg on organbon that has relatively large chromosomercockroaches, for instance-od vstog trulated urtdine us a vanalizing reagent, RNA appears to be formed along the chromofono strands as well as in the nucleolus ( nuclear structure in which It has been thought that RNA mainly forbed) The urn of the out deace favors a messenger RNA, but defalt o evidence to still n alted. To tam up we have discussed soone aspects of the chemistry of the groetic toatettel, DNA Ve have good no come of the current thoughts on tho nature of the code which directs the formation of a spectfo protein. And no here cplored ono soggestion on the wty genetic fnformation is cornmunicated to the appropriate centers of synthest From these coo identians, we go to the problems of the molecular basis of recombloation ·lo an earlier chapter we introduced and discuitsed the phenomenon of genetlo roconbination Classially rocombination rofen to the appearance of now combina tions of trets in tho cell or living argantom The cow combinadons are formed during melons u a consequenco dtba of the rundom utortinent of chrome somes or of geotie echego produced by Crossover. The following discussion will be concerned only with Tocomboeton of linked goretic material Tbe Molecolar Structure of a Geno Jreatag. For In malosis, prior to the first division, intimate patring of tho chromosom / strands (chromatids) take place. Broala in the strends aun the occur and, by rociproal axchange, chromatid sogmenta an bo Tocombined. This ovent, of courto, permits tho rocoobtoation of Inbod genet. For many years, it was thought that noch recombination could occur only between genetic regions controlling dif ferent tratts, but not within a singlo roglo trelf in large part, the conclusion still bolds. It is probablo that breakagefusion recombination does occur prima rily if not solely betwocu ured control ling spedic trelts rather than within a specific region Le between genos, pot within & gezo Although breakago fuston aan bo seen to occur tho malocular basis of Crossing over is unknown. This reflects our ignorance about chromosoanel of ganization in genel and, spedbully 37 ·The Molecular Structure of a Geno our ignorance of box the DNA od protdo ao mungod. Hovora while the problem of chromosomal structura b still largely obscure, picture is emerging of the structure of the gear. To udostend It, o most condder rocombination once again All tho alginal observatiom o recombination poggested that no rocombtration was detectablo to nating in which each participant ar dod an altanatiro allcle of single gode. Vith thos, onceptions atro found. It is now knows that alelas, el concertad arith a stagde fraction och u tho formation of a particular mayme, definitely can undago Tocombinatiam. Recombination com, therefore, take place within a genetic regloo performing a sloglo genetlo function. The problem to whether this tatrageulc recombination is a breakage fudom type, smilor to that cyto logically observed in crossover between geres, or whether it represents something dee Breelago fosbou would imply that fost beforo redoction divblon, when the alleles are very closely patred, boods oro broken at identical portions in the DNA maloculo of the two alleles mod recon- Dected to the other partners To maintain the act nucleotide sequence of both strands, this would have to involve the pbosphate ester bood botworn adjecont nucleotides. Muy difficulties are raised by this ruggestioo. Do the deanyolbosophosphate backbones of the DNA chams over get close onough to cpablo ruch bond breakage? Phosphate groups tro all negatively charged under the normal physiological conditions of the cell, and if they canno close to gether they would alert strong forces of ropulsion. To overcome theo forces mould require great mounts of energy Odo como dary that this a potrblo. The benefit of see, Le, recombmation, are cortanly ruffelent for the cell to call on all reSources. Even were this disculty overcome, socood barriers toboont in the phosphate estar bood. This is a role tively stable bood od also would roqutre considerablo enowy to break and reform Bocus of those od other difficulties (for oumple, consider this problem to relation to coding, rose the dictionary to set up come conso Zoles und came the consequences of breakago-frosku) efforts bavo been made to formulate alternative proposals to account for botngeni recombination. One such proposal to called copy-cbolce, and the res koa for fts formulation will become evident who wo poło samo additional curious facts about lotngente recombinaton Coordder crow of two diferent alleles of gene B b, and by We un represent their position on the chromosomes + b D + b D A by + d o o ·54 Tho Molecular Structure of a Geno The Deles are symbolized as slightly displaced from one another for the purpose of descriptivo clarity Two additona) linked gen A and D ono on either dde of b are necessary to the analysis Note carefully that if no crossover OCCUn between bi and by the b mutant will be recovaod If a dorical crossover does occur between bi and by DOTITI B progeny (c_**_ d) will be formed. However coordng over between b, md be mut also yield recombination of the outdde markers, that is, В progerry should also be mutant for a nnd d The espectad reciprocal recombinant dass i ADD mutant b and wild type A and D Actually in many crosses of this type, one finds normal B progeny which are unerpectedly normal for A and Dwell (genotypically ABD) In addition, in intragenic croes there are cuses in which it bes beco possible to prove that one of the two recombinant clare never formed, that is, elther aBd, or Abb D was formed, but not both. The to referred to as ponreciprocal recombination The fact is then, that nonreciprocal recorbonation does take place within the gene. This means that popreciprocal recombination presumably takes place between DNA molectiles To eccount for this, broalago-fusion in DNA, although certainly potable is unlikely ergo copy-choice. Copy-choice Copy-chatoo is assumed to work to the following made Prior to repllation, the two atrands of DNA incoll to forma stogte strande. (This occurs through u vet unidentified physical forces or is catalyzed by tho oozyme tavolase) Single-stranded DNA then replicates its complo metary strand. An error to the replication could occur u is shown in Fig. 28. Supposo a strand, complementary to straod 1, were to the process of replication. Assume that another strand, identical to A except for en alternativo allelo (strand a) were also in the cell and very close to the Dowly formning complementary rund. The replicating strand, on nire occurlons, might witch and we strand a u it model for a wall region. Tbo replicate, then, would not mirror the parental strend, but would effectively recombine tho gaette coches of the two strund. With the mold, there is no need for brralaga-fuscom or the formation of reciprocal desses. This type of copy-choico itplication abo woolt egin the to combinational events obrerved in bacterial frases or In bacterial trust formation In bacterial transformation for etample wo loow that a mall amount of DNA is taken into a cell, and that a portion of the code it corries, fn sido way can become Incorporated into the replicating codo of the cell. In this case, the copy choice mochanko muggest that the to corporated DNA puin with a homologous region of the parental stradd and se consequence of a copy-choice error in replication, recombles Hon of the traits of the donor DNA and the parental DNA occur ·Ar 71 Copy-chol recomb to The two perut I trud a homol ogoes bot not letel Whother rocombination occurs by copy choice to ouproved. But the facts uro cloar Within coe chromosome, at lost two types of rocombine thon must occur recombination between genes and recombination within gedes Tho mechanism of recombination still mat darllation Strice recombination within a gero does occur we com oso It to map gene, and to try and see what its fine structures Coutenparury finestructuro analyds has been provided by Seymour Berret mbo has also coulched our genetlo vocabulary with tho terms muton, recon, And clstrun the units of mutation of recombination, and of function, respec tvoly Benzer i capedments have been carried out with a bacterial virus, od ho has gono far towerd defining genetic unit at a molecular lovel. Stoco we have previouly md at length descríbod the genetla of tryptopho synthetase formation, wo will continue to wo this game as a model in describing genette flao structura. An Structure As we discused in Chapter 4, un albolic series of tryptophan tynthe tavo mutants an roudily bo bolatod. These are mutations of dogle geno ou chromosome 2 of Neurosport. These allello stratos, If croured with ono Lother, do yield to:frequent tryptophan-.ndependent progtry and now we can map the gonetto regkom by determining the frequency with which different alolic crosses give rise to tryptophan-boxdependent progeny The map on bo prepared by udog tht ono alterion and without attempting the almost super trumman tuk of determining whether the reciprocal des anbo found that I tho geno rith the double lealan As we also documed to Chapter 4 Pro know that maury functional ducenco cun bo observed between the members of this allelic series. Wo am met op a broad casißation of these mutants in the following wwy (Fig. 29) Mutation may ghe rise to either CRN+ or CRL-train. The CAM+Bindlated in the chart, an be fubdivided further into three classes (I) strains which have lost catalytke activity for all three reactions atalyzed by the parental cluyroc (II) struha without atalytio activity for reactions 1 and 2 but with activity for reaction 3, (UI) trains without rettvity for rerctions 1 od 3 but with activity for reaction. Cm Il can be sobilividad fartha In that some of these mutants have no cofactor requirement for reaction 3 others requere, bo contrast to the pertotal strain, pyridkonal phospbate and pull othen reture both BG mod tho ampo scd sertoe ·CRM 19 1 см COFACTOR REQUIBLETS Pedonali More Perdonaro + + (1) Il + + P + werke Tryptophan + morte wa Choment of the mut t From this information, it is apparent that the genetic regbon ca trolling tho formation of tryptophan synthetero bo highly complar I innlydog tho fino structure of the region, therefore, we can pubdivid the region into a large number of individual mutational atos Such muta Honal subdtvisions of a functional area might be condered as mutons A muton, es defined by Benzer is the smallert clement that whep eltered con give rise to e mutant form. A single functional are gone, condata of many mutoos. Since the game is DNA, it is reasonable to inquire wbut tho muton represents lo terms of rucootides. A muton should nopros.com to minimum number of nucleotida that must be altered to permit into add alteration. From his analysis of bacterial vtrus rocombination, koowl odgo of the total amount of DNA per virus, mod come ingeniou hrump- Hanis, Bonzer estimates that at martam a mitou condet of for about treo or four Ducleotides and hopes it is really one (This would fit our code) What about the structuro of u gee to terms of recombination Bozor suggested tho ten recon to define the smallest unft that o Interchangeable by gepetlo rocombination. The analysis muggests that the recon may have the molecular dimendont of ono nocleotide med Hoved, if vartou tryptophan-iquitng mutant Arvind ko croured with one another tryptophan-Indopondent progeny ocadonalty arlso by Intra genlo recombination. Uning orthodox mapping procedures, wo CO DOT map the mutons. It turns out that mutons appear to be arranged to Hoeur estay witbla tho functional gero area (Fig 30) 19to the det, catalo regions en costly susceptible to mutation Datsy reglans) other regloos are impervious in mutation dert regloos) no come ob srmation of interest is that alloles that are functionally under tre pot Attard hroughout the genele bert ze heel in the forta ·2 Schematic repre hou of the outlet Hracho of the tre gone for den type, me fler Car are of tryptophm gynthetase, mutations of class I upeo to be clustered to tho middlo of the genetic area. Mutations of dos II ve found hadded together on the right ddo and mutation of class III on the left ude. Theso clusters of functionally related, highly struag md highly rativo atoes rapond paflclently to mutation to be picked up us fmctional vertantı. What about tho interventog regions of deco? L it moro difficult to obtain mutation there? Or are experimental toob #ll inadequato to revolvo tho effect of mutation in these roglons? This is related to the problem of knowlog what to look for and whillo there are no means to the questions posed, there is a suggestion. It may bo that mutation is fust us frequent in the silent roglom as fin the padsy regions. This would troply that to certain areas of the enzyme, eioo actd abstitution con alter carrymo activity while in other grow pobstitution cannot. To actualy fada Dutation that has no functional effect on the enzyme, we may merely have to grow up a few million somaleppearthg stratra, pretty and Angerjant tho emaye, and see what happens. Elbe that or have a clover den Tho problem wults Sooo tnteresting ovidence for tho above concept bowover comes from the superb Aructural analytb of the protein pyoglobin carried out by Dr J C Kendrew and hit Loodates. By Ytty crystallognphule diffrac too mod the liveliest imagination, it was possible to determine the catre structure of myogloble. The structure is given to Fig. 23 in the work these author achievod a remolution puficient to let them look at the folde within the proteta cald. Ono fact emoryo clearly the protem molecule is folded in psch a manner as to bring into cku spatial relationship UTIDO cd groups relatively destent from ze another to the chate. The at And areas to which folds occur as well as area of straight proteto chun. Tho tmportance of these structum acorder to betaro tro mediately apparent, once there is a great deal of orldenco avadable that permits the extension of the picture of Dryoglobin to other proletas, including czymes. If potions of Delghboring chains of unido acids brought together by folding, coustitute ates of enzymatic activity and other proteins of the molecule, the strught sections, represent only regious of structural support, then I retroneblo correspondence can be et up on the one hand between the Dalry regions of the gene and the sites of erate activity and on the other hand between the quiet regions and the area of wright-chain fructural upport. Lo the Latter case substi ton af one ontoo idd for another bro .th i mulatim in ·60 The Molecular Structuro of o Gone qut ngion eusily could have little or no mencurable effect on CDZYTDO actiut Vlutation in the noisy region, with consequent substitution of an anno acid to the site of enzyme activity could have a dramatic austy Mcustable effect At the present time, therefore, wo can state only that there to still much to be leaned about tho nature of protota folding, what directs , and whother tho gesto effects folding apart from sequence detamation. It must also bo emphasized that whilo noisy and silent regloos hevo bom found in the gwetlo fino structure of tryptophan synthetase, slmſlar regloos have not been observed by Bearzer to the genetic Apo structuro of tho trult ho studied to a bacterial viros The reasons for these differences uwalt reconciliation This is an area in which many experiments are now being carried out, and in which the combined tiso of Wologlal pd sophisticated chanical techniques are belog profitably crploited to gain further insights into the molecular basts of heredity Complementation Wonos como to an additional mod Intrigutng question. Most all the matons of a glo genetic area bo present together and in a prescribed order for a specific enzymo to be formed? We can find out by making uso of a test called the cts/trans test, a test which gavo riso to the unit of function, the clatron. Tbo principle of this test is illustratod in Fig. 31. Baskially the problem i whothar enrymo formation will occur when all tho necessary genotie olements are present, cot in a singlo Inlage group (the ci position) but distributod either between two homologous chromosomes located to the same mucleus or to two different suchel aar red in a contoon cytoplom (the truns position) Surpristogly it appears that all the genetic elements arcessary for Cozytoc formation Dood Dot bo bound togother on the sun chromosome. The term catron will be wed to define the smallest subset of mutons that must be present together to thods podtion, for enzyme synthesis to occur in the call (Wo co dellber atoly smplifying the original definition as given by Berroer but at po sacrifice for the apodtion of the general concept) As so filtration, if thero are 100 putona in gene, assume that the presence of at least 20 Inked motons on one of the chromosomes lo necesary for entyme fama tion. A partition of 19 81 on we allelo rod 1" 83 on the other would not pamit diyme formation. A partition of 19 81 and 21, 79 would permit complementation, + + E 3 The cutron tott Obract WT the traht be aufsted i tre tres com fogwatch or only in the lonfigur tron? The wrotic furents prest has both thes, but diferente cht tributed ·The Molecular Structuro of a Gene Let w try the following type of experiment. If two trate of Neuro spon of amla maung type oro grown together fusion of hyphao between the stratos cum occur and now byphao will be formed that curry the two parental bucle in a common cytoplasm. Tho nocial do not fure to foron a strual phere but divido lodopendently of each other This fuodon straints called a boterocaryod and can bo pen eully If we grow 1 strain of Neuro sport which requires tryptophan together with a strain requiring arginino. If the growth wedłum contato pathar tryptophan no arginine, a hetero atryou will bo formed. Those struins can grow bearuso tho mude that are upablo to form arguddo carry « gene wloch enables them to make tryptophen, and the tryptophan-requiring nude me genetically capable of forming arginine. Thu we have a sort of offboat beterozygote, poco the Hralos lave all the necetery clements for tryptophan od argindno farme too, but distributed between two different poca, ntha then present in 000 nucle. These two mclear types together get along as well u tho wild type by belf These two nucleur types are aid to complement each other A dollar complementation test can be carried out using two allele tryptophan synthetase lets (two-lem) mutant. As a text of complementa thon, wo con determine whether a beteroctryon formed between two tesc less motmt in our allelle verlos to apable of growing on a medium lack- Ing tryptophan. If It Is, an sich a strut form t eso? Cortata cornbinations of alcles do exactly the Tho beterocaryon an grow in the absence of tryptophum ad con form toe. In this case, tho hoterocuryons gror slowly and the amount of enzymo formod te mal, but It is an experimental fact that complementation does occur betwood cortan males and does ropult to cryoso formation. It is open poniblo to mapaDeles to terms of complementation by testing all the mutant In O extensivo allello wries against opo mother The experimental result is that the relativo portion of alleles in a complementation map is stroller to their order to recombination map but the correspondence to pot Identical Thoro two maps must then tell us different thing but retourch on this recent concept hos Dot yot advanced to the point where the differ DOO I understood. But one thing has been learned. Such complementation maps tell w that alleles of similar function do not complaneat. That is, alleles all belonglog to dess all those without enzymatic activity for reactions 1 and 2 but with activity for reaction will not farm tryptophan-independent betorocaryoos. However by this test, momber of doll will complement members of des III, matants with no catalytio activity for actions 1 md 3 but activity for action ? Can wo explain the typo of Interaction tavolved to complerdentation No. But we can speculate Wolnow that many enzymocowbt of at least two Independent polypeptido chalos Bokod topother by covalent bonds (eg SS bridges) and by attractku between electrically sharged groups. Theso molecuks/ ·12 The Molecular Structure of a Gone 1 con disociate. Geoctio salyd tells us that a gede consists of relatively fow dstrons At present, wo gre tempted to predict that a stron may ropresent tho genette eres that controls the formation of a stoglo polypop- Hide chain. If en onrymo consists of more than ono polypeptide the func tiomal gemetto cre defined by the gwoo will then condot of un equal puber of citrons. Eut this is for a reasonablo gues. The statement probably will not survive long, and may not survive publication Summary Wo Dow can antve at the following conclusions concerning a gono A gero is the son to the chromosome to which mutation an occur und affect the ability of the organism to form a spocific entymne. This genetlo orna is a complex region in terms of both mutation and recombination. It can bo subdivided foto many mutors and recons and foto fow cstronk Wo might now define, or perhaps we should say rodefine, the geno as tho entiro functional are required for the formation of a spouifio autymatic Lettvity Tho ustuto reader will realizo that the definition is mcertain. In the years ahead, it is spected that the definition of a gene will con trauc to change for the game is exrentially an operational unit. In the hands of earlier workers, it was first a unit of segregation and then undt of danical recombination. At present, it is a unit of function, and in tho future, it may well bo a unt of DNA. In my event, wo ure Dow beginning to talk about the molecular dimensions of todo of bere hity Although DNA appears to be tho substance that tranenita bereditary Information, we havo Dot mentioned its organation to chromosomes, Tho vhlblo chromosomo of higher farms probably contains all the DNA of the col. Tho ibaitance test Indicates that gedes ke atinged to linear array in the chromopornog of all organisau from butala to How over the linear array can obviously tako many different form. We know that the DNA, fo romo way must bo condens hromovome, saco the total length of DVA, calculated from the Watsoo-Chet model far exceeds tho actual chromosomo leogth. It has been suggested that the DNA 1 arranged in Christmas tree style, with the DNA - Habe aloog protetn trunk. Rectproal recombination then could occar along the trunk and ponreciprocal rocombloudon along the limbs, bart again the only speculation. The band facts are still to be discovered. ming ·lo the proceding chapter, our emphunda has been on the gove itself, its structure and o function odor turn to coudontian of the mechanlos of peso transmission end the lem of heredity to introduco this fubfect by gem tovoking the co operation of our favorite haploid angankm, Neurorpora crane In Neurosport, the vegetattve tranunitsion of traits takes placo exclustvely by mitotic muchos divt dons. As the organism prom, nudd divide, and a tho mraber of mickel in Croes, the Direeltal mess erpuds. As wo already know to a well-beltved mitotic division, without chromosonal Imbalanco ar gone mutabon, two daughter muda kro formed identical to the perent nucleus. Stoco the growth phase of Neurospor haplood, auch das contatos only ono rot of chromosomes. Each cleromopomo differs from all the others in tho Gonotic goes It carria and, therefore, in the met of trall It determines. When gedo mute Mechanisms than occurs to my haploid puceus, an Immedlate tertion of some function to that made out the place Mistetton and Selection Whether or pot sich um deus for vives depends on many factors. To Ilustrate, brume that we have two Neuro sport cooidiospores, ach cootalning one Identhaal mucleut. They differ hortet ho a single respect. In oor of the spore, Dubation of the tryptophan Sathetaso gone has occurred, trductage mutritheoul ·14 Gondhc Mochanisms requirement for tryptophan If we now plece both sporas in an environ Dent that normally permits gamination but that contains do vdlablo Fourco of tryptophan, what happens I owsily predictable. The scoal sporo will germinato to give rise to a deu plant, the mutant part will not germinate, and its nucles with its mutant geng will be lost. Consider another type of mutational event. Astuino that a singlo motation occurs til uno spore to confar upon it the capacity to germinato and to groti moro rapidly in 1 relatively and enviroment. If the two spores are placed in a normel environment but with a climato in which tho moksturo content is reduced, tho matant sporo will germinato and the plant will grow faster than the normal sporo Tho mutunt will atract and utlizo all the resources of the envtronment at a moro rapid mate than will tho normal plant. In ram, the mutant will outgrow tho pormal plant and displaco it from the new environment In this case, tho normal nudous with the normal gene will be elminated. In the above memples, one or the other of the parent and mutant ma wu eliminated. To ertmples, although otowhuat smplified, 1 lustrita a prindple that has been validated by countless observations and aparlments. Mutation and competition in the original or in a now onvironment represent powerful forces to the creation and survival of now Atter genotypes in a haplold organlam Didotke genotic rocornbination also occurs in Neurospora, doce there 13 1 sotual phase. (Note that to Neurosporn, the diploid stage ts transient and give deo immediately to the haploid plant, to humans, the completo roverso is true.) To form a gerul zygote, two cells from struns of oppostto mating fuse and form diploid cell. Each of the haploid puchel contributos set of heplold chromosomes and a cell cootaining two such sets is formed. Such a cell ts diplodd It contains two godor that govero evry spociflc tratt. If the two Lots of chromosome are identical In gene con tont, the diplodd coll ia culod homozygous but if the scta differ-that kn If there are alternativo Teles of certain genes in the two sots of chromo comes the diploid coll ts vaned haterozyrow Tho tarns homorygous end heterozygous an also refer to a gene A diploid cell with two identicul alleles is homozygous for that particular gene if the allela differ the cell is heterozygous for the gene As we mentioned before, melosta permits resistortmont of chronovomes. It ako permits croostng over betwoda bomologoru chrono one. Mielosis, therefore, is a sexual mechanbim for the recombloation of gees contributed by the parental strains. It permits the ready formation and trumsalon of new gente combinatioot. We might way then that the life cydo of Neurospora permits the evolution of now types by ut lout two mochumkums. Nor genes with now functions can also in the hapload orgardom and be immediately crpressed in its tunacleato con diospores the second mechanison pamits recombination of these Dow goes with the gma already present All these to the bo rubjected to the test of ·Gmetre Machant the environment, which can select out these genotypes best fitted for the Enviromcat Bacteria Reaanbiration Wo hayo ibow bow new geno combustions form by genetic recombination to an organism that enjoys melust Tho boquldog mind, however Toght wonder about those orgmisons that spead thet enthro Hfe as haplolds, organims such o bacteria md bacterial viruses Camargmions nch u there ako mdergo genetic recombination or mut they evolvo now genotypes by mutation alone? Empalmental work of the past docudo hos down that bacterial games are linked and mut therefore bo organized to structures that are similar to the structure of a chromosome This fact ho beca deducod from genetic aperiments, althoogh it has not yet been confirmed by cytological otanination Escherichia coll mod Salmonella typhlmotum are comples of two bacterial spodes which characteristically contain one linlage group and kro haploid. Vegetativo reproduction takes place through duplication of the bacterial chromosome ad tbe trommlakon of op klental chromo komo to ach donghter collo suspect that this event o smile to mitosis, although this conclusion lacks cytological confirmation As wo will discuss in a momoit, mutation plays a major rolo to tho evolution of dow genotypes in these organisms. However bacterie are also capablo of rocombtntog tho geetle traits of two separato cells. In bacterial transformation (100 Chapter 2) certain bacteria can take up parlilod DNA from a genotypically different cell, and the dew Information curled by tho DVA co bo mncorporated toto the rolprent calls own genetic sp paratus and transmitted to its progeny In transformation, therefore, cell la formed that an be alled, with one charity hetetuerygoun. Noto that It is beterorygow for only a mal region of the genetic structure, in other words, e partial beterozygote. Unlilo the formation of diploed cell lo Neurosporn, in thosformation the groete contribution of the two parental cell Hoes to unequal, and recombination may well result from a copy cholce type of replication Regardless of the mechanism byvalred, bowcrer recombination such u that dosalbed for bacterial transformation clearly does occur mod the formation of partial beterorypotes is characteristic of genetic recombine ton in the bacterial world to general. It is the mannet to which dooor DNA b acquired by a recipient cell that varies In trasformation, the donor cell DNA to pided up from the pedhim. Another mechenden for rocombustioc, bacterial conjugation, wo discovered by Joshua Leder berg in certain strans ta E. coll in these anim, tid cells to fuse and forma cytoplotnic bridge The chromosome of the donor cell to then Infected into the recipiat all. Bacterial conjugation requires a matte typo nuem, strict cells of only wound (FI) con kive a donors, whilic ·Gonotic Mechanism other cells (F-) SETVO us recipients The difference between (H) und (F-) cells is still a mystery Surpoidngly aaugh, ove under condi- Hons in which a cytoplamlo bridge is formed betweon the two calls, the entiro gtromo of the donor coll is seldom injected. Again, tho rodfptent coll is only partially dipboid. After conjugation, the colls separate, and rocombination takes place between the genes injected by the donor coll and the genes present in the rocipient chromosome. Daughter cells bour ing now combinations of the two peront cells are formed, and tho non combinations are transmitted to their progeny Sun third mechanism for recombłoetion, bacterial transduction, alsts to bacteria. Bacterial transduction differ from the other Icchantom In that the agent for tranzmitting 1 portion of the DNA from odo cell to mother is a virus. It may be somewhat disquboting to think that a viro, the very model of e cell parudite, can transfer its bosts DNA froen opo cell to another It does occur however even if unei pocted. The story is briefly this. While muoy bacterial viruses appear to infect and tovurlably destroy the spoctito bactertum they perultire, other viruses behave differ ently These can and do infect and destroy bat, mder como unorplated circumstances, thoy Infect cells and then turn benign. The viral DNA becomes attechod to the chromosome of the bout cell and multiplies when the host chromosomo multiplies. If a vtrus hus this characteristic, it is known as a temperato virus. The condition whereby the vtral DNA HU quietly on the host chromosome is called lycogeny From tme to time, tho virus spontaneously erupts (by now you Toaltro that spontaneous fn btology moans who do not know why) reemones to malignant foron, multiplies, destroys its host cell, and pours out roady to tnfect another bost cell, prepared either to destroy it a to lvpogenize. When the DNA of a temperato viru in z lysogenic condition Is activated, It forms a completo virus It can then lyxogenize u dew host and any a plece of to old boats chromosome into the dew bort Aloreover the genetic information of this chromosomal fragment can bocomo tncorporated into the Dow host. Bacterial recombination therofora, characteristically takes place through a number of different mechanisms, but only partial diplod cells ero forned, and copy-choico may be the polmary mechanism for the in corporation of the now information. Tho absence of equal genetic contribution and the absence of a true redaction division distinguish bac torial recornbination from that formd to higher organismi Ono of the many enigmas that surround these various forms of bacterlal recombination is the role they play in tature. Do they represent laboratory odditios forced upon naturo by the Investigator or aro they crucial to the survival of cell? And of equal interest are these aclusively bacterial phenomena? Ile know that human cells are susceptible to cer tuin types of virus and that they can also harbor viruses for years a coord- Hon soalogous to hysogeny Do human viruses arry DVA from cell to ·Genate Mechanism collaod, if they do, why? These pralements pro not meant to glorify tho state of tho question mark, but to give you some idoe of the thing that fatiguo biologists at the moonent, and of the thing they are trying to lam. Therefore, although we know that bacterial recombination can occur its rolo in the creation of new bacterial type bas still to bo spread At the present time, it would appour that mutation and selection o tho major forces tnvolved in the ovolution of Dow bactedal call types. Wo how that mutation occurs sponteneously md to all gator that bavo boen studied, although the spontaneou nuto of mutation among gena appoen to rury In general, bacteria pre Anglo haploid colla Mattoos kro rapidly cupressed. Moreover heplold organismos multiply very mpedly u compared with the higher diploid form. In the laboratory under nutablo cooditions, the bacterium, E. coll wall divido about every balf hour At the end of 18 houn, one cell will give rize to 10 or about mo bhoo cols. This means that mutant populations to cully bo crprened, and selection of Dow genotyper by the environment conceally occur Wo havo Illustrated the principlo of mutation and selection culier in the chapter and will now discutono additional compile which bas capo to our atten ton rather forcefully to recent vean. Excherichia collis ordinadly killed by tho mtidotle substance, streptomrydin. If treptomycto added to a culture of multive cells, the cells will be blod. However Ecoli contatos a gene which can undergo mutu ton and confar rentance to streptomycin upon cols that any it liuta thom to streptomycin redetanco occa spontaneonly about once to overy 10to 10 cell diviatons. In the absence of streptomycta in the coviron met e mutation from streptomycta populvity to stroparycin Taubstanco will go unnoticed by us, and apparently also by nature, since tho Arepto mron-raabtant genotypo does not accourulate to any noticeable cutent in normal populations of E. coll. In to presence of streptomycin, bowover only those coll with tho robstant gone can purvivo od grow and the streptomyco-estitve population erudieatedIn a world Aled with Kroptomycte, the prutant gepe becomes tho pormal gede Thou son mportant and contestporary problem. The microorganiom has a remarkable genetic Beddity the potential to mutato and meet the cullenge ofare unknown enviroments to onda to survivo. Io u stolar way us you mut know the illes bero conquered DDT od pow manh comida tog whether bo con conquer the looling neditions and the Prelghtlemen and the new challenges of space Diploldy Tholas of genetla icre formulated from the study of higher planots and animals. Then organlos difer from fungi od bacteru to that they 20 diplokt und krvarlably posted some form of semnal reproducttoo. Typically a pow indtidoal urbes by fusion of tho Donddotical gametha ·Gontic Mochan ims calls, the egg and the sperm call. Fwlon results in the formation of a diploid coll, which, by division, growth, and differentiation, glves rise to a now adolt Reproduction, therefore, requires the formation of haplold gameter from the diplod cells of a maturo organism. The formation of progeny consists of two melotic divisions, ono in the male and coe in the female cell lines The fact that is the diplold type of lfo cyclo e now Individual akses by fusion of two non dentical garpotic cello soggests that rocombination plays a mafor role to the formation of now types. Tho formal genetics of diploid organisms differs fn certain respects from the genetics of haplotd organisms. In diploid genoties, the observeblo charecteristic of the organism (the phenotype) derive from the cristen.co and copression in each coll of e doplicate set of gones. Furthe allellem implies that for any given gone a heterozygou condition can odst. This raises the problem of the phenotypic cypressdoo in the organism of moro than ono allele To illustrate this problem, let us choose a microorganism, a yout, whoso vegetative growth phase de diploid Docal anco Diplold youst calls divido by mitos's end can also undergo medosis to form haploid cells Tho fusion of two huplald coll results to tho roestablishunent of the diploid line. Two haploid strains both anpablo of forming tryptophan synthetaso (t2x0+) upon fusion, form diplold coll arrying two tasot genes. Two haploid struns focapable of formfog tho antymo (tax-) fuse to give e diploid coll lino with e nutritional require ment for tryptophan. In a fusion between a taso strain and a tuso+ strain, the diplodd lino Dow carries both all les, on ono chromosomo la a geno that can direct the formation of the entyme, whillo on the hotbologorus chromosomo la mutant allele that cannot. The phenotype of the diplald coll line, which is heterozygous for the tryptophan synthetase gene, bs tryptophen independent. The cells synthesize the crtymo and can grow in the absenco of added tryptophan The Asset geno is aid to be dominant Over the taso-gene In general, tho abflity to synthesize un active enzyTo qualifies a geoo e dominant. The presence of a dominant gone in the diptold coll also wually parroft the formation of a specific enzyme at a rato sufficient to allow growth, although not necessarily at the maximum postible rate. This cumplo Ithustrates tho problems, however that can arise as a consequenco of beterozygosity For instance, e mutation in the tase+ gono con result to the formation of 1 mutant enzyme that might in some way inhibit the normal enzyme. This would lead to a requirement for tryptophe in a heterozygoto containing a Dormal taset Lele In the absence of other knowledge, we would then conclude that the mutent gene war dorinant to the normal allele The relationship of dominance and its converse, reccedveness, the ·Genetic Mocha ions conxquence of tho fact that ti diploud cells, ach me of the allelos auta its own action and the phenotypo must reflect the result of thetr Interte tion. If one of the alleles con function and the second allelo crot, and to neutnal, the forma mould opear domment If the second aelo inhibits tho Letlan of tho first, the rocond would ypper dominant If ono Jelocita direct the formation of a product but in torufficient mount, tho hetero Tygoto appears intermediate, and dominan.co lotermaato. Mony interactions are poorblo and all are found on the lovel of the organism, a homkutygodhe organism by definition, one in which all the gede patrs are idential, whilo a betonozygou organim ono in which a variablo number of gero patrs differ All gradations between completo homozygodty and completo heterozygosity odst, and allollo interaction b a probleme beric to all of diploid geoetica The fact that a vegetativo el carriles duplicate genc confers genetic stability an all, and thus may bo upo of the reasons that the majority of higher plants and mimals aro diploid In Lapland organism, ruch as Nourrowpon and bactale, mutabon an lead to the mpid phenotypake a pression of the mutant Talo In a diploid orgasm, however expression of rocoustvo prutation requires that the mutattoo occur at least twice, ether in both members of a diplod pelr or singly bo two diplold genomes followed by recombination. If the probability of mulation of apo member of a garo pats is 1 to 10 col dividons, the probability that both member of the gedo pur will mutato in the same cell at the same time se product of this probability a 1 la 101 cell dhuinons. This rare event In addition, I tho urutation occun separately tho mutunt allokes must find each other or they may be lost in the erotic shuffle. Thu meny mutations can occur in a diploid organism and pes - detected during the vegetative propagation of this organice. The strato an amply grow and tumulato recentvo mutations. Occasionally double receptive will be formed, and the phenotypte etpression of the gono am then be observed. If it to valuabla, wo treat tho aryanbom and tho puront lines with great deference. If it b troublesome, wo try to correct a liminato It These ao camion practices in horticulture and commal husbandry Whilo diplody coafas great stability co vegetativo reproduction rea combined with diploidy provides the opportunity for a species to try out Dany Dew gene combinations To see bow this worla, let o consider tho thun nision of trato la diploki argoma kk the tru diplota cell lines both undergo Delosts and form beplold goneter Thomson Agrume that too!! Ibas differ to particular tralt, chrymo formy Hon, and that a dominance relation bald Let E represent tho (dominant) too which direct anyme formation (emrt) In the phenotype, and o ·ho Gonetic Mechanisms Toprevent tho (rocentvo) mert alele. Assume that 000 organion hus the genotyp. EE and the other or Acros between the two will gtvo the rosults outlined in Figuro 32A, where P stands for parent, G, for gamoto produced by meloods, and F, and F, for the first and second flllal gen antions. In this cute auch parent prodaces but one type of gamete, and all tho F1 progeny aro alike, E. (emat) A cross of two Fjorgeoisms is diagrammed in Fig. 32B Hero, otch Fi gives rise to two gameter. There are Croally produced in oqul momba Random fertilization means that fusion of any gamoto from ao cell Hao by my gameto of my other call loro is equally probable. Random fertiliza tion of Fi gameto produces threo F, genotypes in the ratio shown in the figure. Stace both EE md E6 are (ant) there are only two phenotype tn 3 1 ratio In the Po noto the reappearance of the two parent types, EE Add ac and the persistence of the recoonbbsent type, E. In diplold gonotion, a 31 phenotypic ratio in the F, is a clear indication of a singlo-gmo diffaronce. NE х :00 do E E F & Fig. 32. The inhent ca of Ungle go. (A) Ming homarygous domis at nd honorygou receive (B) M thg of F het ro- Tygotot 1 2 NineTimerThreesome Let w now analyzo e os involving two gene differences Stoco in this book wo love enzymes, lot the truts controllod by the genes be T= the presence of too (teret) t = not use (te) H = the presence of hetidaso (het) k = x hese (hevo) Aame that the Ted # Stres ard on reperto chromosomes. Tho remults of a cross between the parental types, TTHI X tthi ano gtvon in Fig. 33, . the result of the Fi cod. By now you havo all the Information necesary to calculate and confirm the ratios and the grootypes given to Fig. 33. Moveone you an backaross the F, to ether parent mod predict the results. You cin check your answers by referring to ury of the standard tortbooka given in the bibliography The appenaco of a 9331 ratio (with dominance in each gmo) clearly indicates the kogregation of two unitnked gener ·P THH 6 TH H F TIH F crot TIHE ܝܙ TH TH TH ТА + T. 1 TT 1 HHH 1 TTHH THHH 2 THA 2 HHI 2 TTHA 2 TIHE 4 fortythony Mon ) Houthan F 11 The intentence of two go on aperto chroom وعملا For our third cauumple will analyze the transmission of two genes Hnked together on the same chromossuba Chrom Oromo asortment during mold would by tself not result to the operation (segregation of loked gaan. In the absence of cromover all the progeny would be phenotyp! cally md genotypically like tbets parents. Assume that the tryptophan and histidine geoes are Hoked on the go chromosoDO. A crout of the honorygous dominant (T2/T,) by tbo bomozy Fous recessivo (th/th) with giro beterozygou F progeny (1H/1h) (Fig. 34) Alotos to the heterozygous progeny Wl normally result in the forroation of only two types of sunetes, (TH) and (th) Thus, tf two boterorypowe F, prostory iro croned, you will find to the F only strains thet are (T.R/h) (7,4/1,) and (th/th) all pbeotypically hike ono or the other parent No segregation of the parental genes co the chromocomo hos occurred However wo died in Chapter 3 during roetods the fattorato patring betyron bomologous chromosos permits the occurrence of reg mental exchanges the phenomenon of coalog over the consequences of Crossing over at en sned frequency of coo lo fire, are gheo to foli to Fig 31 By eteninto the figure, you will notice that all the F progeny uro domtnant for both gerxes, us hi truo of the F progody that also when the stres ure to woparato chromosome The difference, hou ever is that both ·TH 1 TH TH TH Part 1 Porent TH TH TH TH Cromov No crouch (Ames) Cronor Moreover (Amin) f 1 + Random fortbrotta TA TH TH 16 TH th 2 TA TH TH T 32 1 th th TH 16 2 th 16 6 Protyper: tar دم - 10 towe AL - 16 ta - 10 Parvatel phenotype done Recommon phenotype don Moto que reciprocal con bhotion) h 14 The watoto to kod got dominants are still on one chromosome. In the F Tou, recombination of tho dominant and recesstvo goses takes place through crosslog over (Have you noticed that crosstog over in the perental chromosomes hus DO genetic effect?) Tbo types of gametes formed, thetr froqueuckes, and tho full genotypto md phenotypic consequences of random fertilization are recorded lo Fig. 34. Note that nlne different gerotypes are produced in tho F, by the brentago-fostom recombination Cenes oven when linked 73 ·Genetic Mochanioms 7 do togregata. Thus the final phenotypic ratio with 20 per coat (1 in 5) Croacing over 61 10-10 16 far different from tho 9 331 natio capected for unlinked goa. Study the figure carefully cod devote some thought to It. Sot up tho folosing problem н th х ти Acuno a 90 per cent crossover frequency md solvo It by writing overy romlag gootype, pbalotype, od tho Ipocted ratios. (For cur histra- Hou, a closxover frequency of 20 per cent wu sumod, but remember Hat the frequency is a function of the distance between the geoer on the chromosome.) You will bom podtion to understand some of tho feecnrung work that has been done, and is will being done, to the garela of higher organlams, fin breedog and selection in toxect popolatkam con trol, mod in the effects of radiation. Sex Determination Boforo wo go on to a study of human geneha, pre murt discous two padditional pubfects the genetic determmation of son and a curious ovent, chromosomal donduruction, fint obxerved to studies on se determine tion. In microorganbm, ferual reproduction arbres from a mattog-typo system. In general there are no mportant morphological differences botween the mating types They are charactertzed by the fox that strung within a mating type aro mutually infertilo Strains from different mating types will crossbreed to form a partial or complete rygore. This compatibility difference is therited as a stagle-gene differenco. In true son wality clear functional and structura diferencer oxist Thero me two gimotic cells of differont function, the ogg cell and the sperm cell, mith elaborate functional differences between the wdub of the two kein. JD htumans, many dovelopmental differences are known to eat between the Band, and these differences appear to reflect the action of many different gepa, Lo, ker dettrmination is multigenk. This u bordo out by the fact that mea determination bvolves a chromosomal difference with it full compleet of geniet. The chromomual bel of a determination co be sen clarly in the fruit fly Drosophila Cells of the female have four bomologous patrs of chromosomes, whillo cells of the malo cootam three homologous putra (antosome) od ono ulile pair Tho milo pur coast of one chro mocome that ts homologous to one in the female cells and mother that to distinctly dissimilar and found och la melo cells. The chromosome found to both cells is called the chromozome, and tho muke chromnomorne caracters the of mele cells balled the churcxorde Females aan trent not only I chromoODO, while males transrolt elther Yor Y and In equ ·24 Genotic Mochansons froquency Clearly then, there is an equal probability that a newly for Hlized tygoto will contein other two X chromosomes, 2 now fomul, a mo X and ono Y a new male, thus providing for equality in numbers of both face Tho chromosomel basis of re determination la men is caperically storlar to that in Drosopbilla Tho feu ulo has two X chromosomes in her colls, the malo o X and Y This chromosomal distribution, bowever is pot untvermel. In some organisms-the domestic fowl and somo moths-the malo has the equivalent of two Is and the fomalo the X and Y In still othen, the female normally has two sex chromosomes and the malo only One-there is no Y chromo come and there are other variations. The rolo played by po chromosomes wu clarified by a study of Dondisjunction by Calvin Bridges. He found that on rire occasions, dur ing medors, tho I chromowana putred, eu cpected, but then did not reparato did not distoin. Thoy both wont into one of tho riccoeding daughter cells. The other coll did not receive an X. All the other chromo soms wero well behaved. These eggs, YX and O instead of the normal, were then fertilized by either or Y from the malo to givo W WY OK and OY In Drosophile, X doveloped into an infertilo ferulo (called a superfemalo-unfortunately a most inapproperlato term) XY was a fatilo femalo, OX e sterile male whilo OY wus lethal, the egg did not hatch It is now known that Dondisfunction om occur in many organisms, tocluding man. Of particular tnterest is the fact that it apparently ain Involve any chromosome. The revelations provided by studies of nondisfunction in mom in terms of both sea determination md the develop mant of physical and mental abnormalities will be discussed in the deat chapte ·History tells us that act very kog ago men thought of his remoto plant us the center of all things with the rest of the universo Tovplying respectfully vroud It Sdeo life inquiry at damolls bod this bull conscelt but not mans ego It no wonde that he has made human genetic a subfect of special boterest. And it is in this part of genetic that ho poede fogenulty for to obedience to cultunl reqatro ments, he mug dory himself the free we of a valuable aperiental tool, con trolled mating Direct stody of the genetic best of bron truts bas depanded largely oro fined statistical melyn's of geroologioul Hide and the compilation of vital statis ties These methods have been forced upon w by the long reproductivo codo to mail, about thirty yanni per goderation and, in the genetlo sense, by unrestricted mating. Fortunately all the accumulated oricence Comforms tho proposition that Gones the transmisdom and function of human and Man genes correspond to those of other but parental plaid organisms. Let us begin with an atmination of tomo very recent daba dedved froin to tnbrodoction of dow and proonblog pothode Tae Chrnos Laple of Go Trombo: Surprisingly the number of chiro mosomes characteristic of the buman spo ces he long been a pobject of contro rasy Ideaubation to discul beanse muesy of the crocosmes ue estoket ·Gonor and Man cally allke while others are small and difficult to detect Recently buman colls have been cultured to the laboratory by techniques (touo culture) dimilar to those used with microorganisms, and, under these conditions, they provido excellent material for cytologlal investigation. By special methods, cell division an be arrestod and the chromorcones maintained at the most favorable point for observation on the equatorial plano just before separation. These studies reveal a bordo chromosomo number in man of 48, consisting of 23 pairs. Calls derived from fomala show 23 homologous pairs, whillo call from mala show 22 pairs and a twenty-third petr consisting of an chromosome and e sbortoped Y (Fig. 35) An im mediato result of the development of Hero culture methods was tho discovery In man of nonctisjunction Some Congenital Diseases and Nondispector It has recently been found that Mongolism, a vrlotus Dourological disorder accompanied by a characteristic Mongoloid appearanco ad by mental retardation, is associated in many cases with a chromosome count of 47 Tho raro child with 47 chromosomes u geoerally born to parents with normal counts of 48 The most reasonable gplanation for this aber ration la pondisfunction. An egg cell in which one of the chromosomaan putns does not separate during melot's would, upon fatiltration, forma zygoto with 47 chromosomes, 22 normal pain and 1 triplot. In Moogollon, the triplet normally occurs in chromosomo No. 21, and, for some use ploped reason, the additional chromosorno alters doveloporrent and results In the dekribed neturological disorders Noodisfunction of other chromosomes including the xx chromosomes, hu bocu found and bs associated with othar disorder. Individuals aro kuona whose colli auty two X-chromosomes and co Y Thoy suffer from a neurological defect known as Kletnfelder s Syndrome and show physiological and psychologionl abnormalities relating to se determina tion and expression. Nondisfunction of the sex chromosomes implies an interesting consequence. If pair of chromosomes does not separate during medosis, then one of the products af metost gets both chromosomes and another should get none of the chromosomes When fertilized, the latter would have a chromosome number of 45 and be haploid for the missing chromosomne. This has been verifed. Individual have been found whoto cells contain An X but no Y Phenotypically they are updeveloped females with Do ovarian tertes (Turners Syndrome) In addition to providing evidence for bondafunction, the discovery of XO offers sono interesting revelation Into sei determination to mm. In Tablo 1 are listed some loown gootypes relating to the res chro mosomes and the corresponding phenotypic epreulon In both men and Drosophila

·1 2
314 5
X
7 8 9 10
11 12
&
2
My L. (Right) a sorrotype
of bum
heal ho
ng ma per corona
on Wow) Motorko
od of the durar motor
d'hommes all I lotte
correty Dr J HT
13 14 15 16 17 18 19 20 21 2

·1 Genes and Man TOT Tho Phenotypic Expression of Marous Genotypos n Mon and Drosophila Gootypu - X UF W M Haren Frutt Fly F F P = Formato lule UF = Updovokapnd Female Notice that in man, X and XX aro fanalo, whereas the possession of only 010 Y suficient to confor the malo phenotype. In Drocophifa, ono X with or without Y is male, while XXY is female From this and additlonul ovidence, it uppoan that Y in Drosophila cules fow if any ganet and noso required for malo development. In homens, the goes carried on Y appour to act a povorful influence tn sex determination, a to attested by melo with the bizarre ctromosomal constitution, 5X,Y In general, it can be concluded that the posedon of matra chromosomo ar tho omission of one of the chromosoma leeds to developmental abnormalities Thore 11 no aplanation for this but there to como intarestog speculation which we defer to Chapter 8 Our discussion has touched on but a limited part of the ovidenco available from Intensdyo researches now under way into the chromosomna! bubs of human herodity in the future, many more instances of the asso clation of spodific disease pattern with chromosomal timbalance will probably be found. We knop bo treatment for this type of discom, Pear haps one day it will be posshlo to prevent ponderfunction or to rectify tho physiological consequences of nondistunction onco It bes occurred There are not idle hopes. Other human disorders with different genetic basis are known. By making wo of the facts and principles discussed to the procoding chapters, we have boen able to establish a retional courto of therapy in some of these cases As an Illustration, we will discun discuro called phenylketonpria Phoryttstowedo In tho 1830's, It was observed that unusual amounts of a compound, phenylpyruvic add, were excreted in the wrio of certain patients afilictod with sovero mental disorders, unully Idiocy or imbecility Tho disouso wus called phenylketonuria and appeared to effect members of the uume fm- Ily A more detailed malysis of the pattern of family distribution tamod up a result one pected at that time. The inberitanco of phenylketonuria could be a plated on the basis of stoglo-gere difference. It was found that phenylketonurie occurred in brothers and sisters of affected parou, but neły in thetr parents or in more distant relatives such as uncles kunts, and cousine. The disorder was unusually frequent in consanguino ·Genn and Man ous merrtegen, Lan, those between cousin-cousin, indaploce, motocphow (You realize that consanguineous mates have a common mcostar ) Fur thermore, oven to affected funktes, phenylketonuria weto in the midority The observations all pointed to the resociation of this dress with a rocentve allolo of Anglo normal gera Threo garotype could then eadst In the population, the bomorygous dominant with a normal pbasotype, the hoterarygota, ako normal, and the bomozygous rocoastre, the aboor mal phenotypa The bomozygous roceutve condition accounts for the lo- Tourod frequency of the discute in coogingutrieot marriage, enco tho probability b baretaod of 1 mating between two hota aygous lodtridoals to give the requtrod bomozygoma recenstva Once the gectia of the trans miutloo of tho dbouo had been solved, the rest bocuno matter of Hochanical dotoction. Tho biochemical basis of phenylketonurla Hor in the metabolism of tho amtoo add phenylalontoo (Fig. 38) Part of the phenylalanino wo ingert in our diet i Dormally omdired to mother anino add tyfodido. If, for FONDO Town, the coddation is blockad, phenylalanine i altanatvoły and dood to pbacylpyruvio add which is then concretod. Combine the gedetto ovidenco (a stnglo geoo) with the loss of a single reaction and our mos piclon fulls, coroctly on an enzymo. The rocedve allelo comot direct the formation of the enzyme that antalyzes tho anvenzion of phonylalando to tyrorna. But how can this singlo loss lead to mental topalement? Human beings are imablo to syntherzo many amino acids contial for protein formation they must obtain them to the diet. Phenylalatoo 1 ooo of these requtrod ambao walds, but tyrostno in pot, since a sufficient Amount of tyrodno le ordinanly forrood by the condation of dietary pheory! alantne. Tho naamal dilet, bowover prandae both phenylalanino and an OH CO OH co -CH-C-COOH wood 1 1. 1. Wochemical bent of phostoxurle ·80 Gender and Man adequate tout of tyrosine, and thus the genetic loss of ability to con vert phenylalanine to tyrodno does not Impur growth. By Itself the loss of the onzyme should be harmless. Horvever since phanylalante carrot bo converted to tyrosine, an alternative mechanism takes over and causa the production of aboammal amounts of phonylpyruvic acid. The accumu Lation of phenylpyruvic acid, a secondary consequence of enzyme loss, appear to be responsible for the neurological demage The course of thaupy evolved for this discaso make use of all tho Information outlined above If this disorder involves just the One Chymatic defect, it should be possible to rear such as to divdnal without attendant montal tmpatrment by maintaining dietary levels of phenylalanino fust mufficient for protein synthesis bat low opough to keep phenylpyruvic acid at u minimal and hopefully nontode level This treatment has only recently been app kod, and the data gathered so far aro encouraging Phenylketonunc children reared from birth an a carefally prepared diet containing subsistance levels of phenylalanino appear to grow normally both physically and deurologlaly Observation on their progress are still contmung, and there is reasonable hope that tho divesse may have been clrcumvented. Phenylketonurla offers a valuablo lesson when we are conaidering the effects of geno mutation. A genetic change that affects a specific btochemial reaction may indirectly being about moro otten.dvo blochemical changes than the low or inhibition of one reaction. If a call lose its por mal ability to carry out a reaction, tev A - B compound A may acct mulato or may bo metabolized to other compounds. Either event can have A profond metabolto effect and must bo taken tnto account when assos Ing the overall phenotypác effect of a singlo genre mutation. Pheory! Letonurla also makes it clear that if a human aborder can be shown to cotespood to a single gave difference, there is a strong probability that the differenco between a normal and an abnormal individual ts basically a differ coco in a single enzyme If we an recognize the reaction, wo may bo ablo to bypass the geartis defect. The Inheritance of galactosernia is another cuse to point Galactoyenil, a disease first noted to children, is therlted on soglo-gone differ coco and frvolves the low of a stoglo known entyme. As to the case of phenylketonuria, wo find that the loss of single blochemkaal ronction todirectly leads to a number of associated abnormalities, including mental retardation. Knowledgo of the brochemical basis of the defect egalo per mlis rational treatment. The interested student can readily find tho details in a reference glyon at the end of the book From these comples, we am see that the basis of geno action to aum, control of biochemical reactions through the mediation of CTIIVTOO formation, I tho samo us that to microorganisms and other subdivisions of the plant and animal Ungdoms.

·Gens ond Mom Slaldercell Anemia In the cores cited above of inherited disease in man, we drow on information gathered from other sources, potabły microorganisms to clarify the nature of the disease and to preselbe treatment In turn, a sorber of belliant studies on another human direne, steklo-cell merla, has olgolf.chotly focused our knowledge of gene action in all agents. In 1919 Lint Paoling and his collegues discovered that the forme Hon of a boormal bomoglobto appeared to be the boochemical bests for the inherited trudt, deklo-cell mornia. As you know bemoglobin to the major protała of red blood cells. It combines with orygen in the lung md carries it to all parts of tho body In general, a decrease in the amount of atmospheric cryge has no effect on the red blood cello of normal fodtvidual. However It w doted u aanly os 1910 that anda these condi thoan, tho red cells of some peoplo become cloogated and take on an odd deklo shupe. Ordinarily tht does not affect the health of the individual, but in como auc red cell sichling is wroclated with morao bemolytic uscada. A study of the family dostribution of red cell dickling dowed it to be inbedted a single roceulve gene. It was ako possible to disttagulah boterorygous Individual from homozygous recentves, doce heter caygotos show shekling bat do tymptoms whillo bomozygous recessives show dcting md ruffa frou bemolytic meania A family pedigree of the disease is given tn Fig. 37 Pauling and his collaboratory boolated the bemoglobin from normal and ackled cells the latter from homorygous rectastves and discovered that the two hemogloblos difered in the electric charge on the surface of the molocules (Fig. 38) Tho bemoglobin of the heterozygoto was T7 0 Or O teor you dor nort Php 17 Pedigru of wilt dintre (ather Net o Herre kotya ·Nornd Suchbetrott - Pg. # Bustrophorette bo Mayor of nou humu hemoglobin toime olt Norm harmacy gou don net wcile can Frit-hat rorygot och Call nemihomorygout OCHY Avtor ndrcato refere a pount of orlom Siche celorenja thon isolated and found to be cotaposed of about equal amount of both normal and abronnal hemoglobin (nico dernonstration that both allchen weto functioning hodependently of each other) With tho bolp of finga printing and amino acid sequence molytis u derarlbod to Chapter 4, Var non Ingrum showed that the tivo hemoglobtus difered in ond amino acid out of about Ave hundred. Ode glutamic and readdue tn Damal bomo globin, HC-C00- Ad 0 -CHis replaced by lysine, HC-CH-NH,+ Hd HO 0 NACH C doc to precisely the same place to the protein to gtvo skeldocell hornoglobin. Tho amino Balds are written with the charges they would have in tho red coll, and explain the observed change difference. As for a can bo determined at present the substitution of glutande acid by lysino is tho only differenco between the two honoglobiors, but this substitution has a profound effect on the physical characterlatics of the formed protein. It realto fo the alteration of electrical charge as well as in a difference in biological activity namely the transport of otygen Vav Tocent tudies of other human herboglobina have brought to light other single amino rod diferences, puggesting thut multiplo allellom to o widespread to humans as in other organisons.

·Gands and Man Kotiple Alcas The most string cause of multiple allelism to man occurs in the goods that determine bts blood types Blood characteristio differ from fordividual to individual, and one can observe this by a simple test. Ait e pample of red blood cells from one individual with rerum from mother (it vuala probably be advantagoons at this potat to retead the sectiom trommtza ton to Chapter 4) A diferenco in blood type between the tndividuals will bo rovouled by the clumptng of tho red cell to the rermm. The red cells will form largo aggregates md settle to the bottom of the tube This pho Domedon is called agglutination md todiantes Incompatibility betwoen the bloock Agglutination can be reon to the test tube, but l ako octu to the blood stream, Le if blood b injected from ano ndividual tubo. second md the blood b focompatble, aggtattratton of the red blood cells of the door will occu Sinco agglutinattom can be fatal, areful tests mat be made to determine what blood mry bo safely used to tranfusion Agglutination requires two components i component in the forum and a compooent on the cells. The elements to the serum that u con cerned with specife agglutinatiog activity are allod antibodies and were daxibed in Chapter 4 Tho spectfc properties of the cell that enable them to react with otibodies are antigets, and again these were discussed In tho earlier chapter When the cells and the serum of two individuak, A and B, oro mfied in all poseblo combinations, the cell of A when put into the stl of Adve do egglutination Cells of B added to the serum of B gtvo Dogglutination. But cells of B agglutinato in the serum of A mod, redprocally cells of Aggluttoate In B serum. All this can be er plained by assuming that A individual have o Amigen on thefr red cell mod havo motibodies to B to thet ktum. (They have no A antibodies to their serum, duce that would borulddal) Similarly B todiricuals have B antigen on the red cells and mtibodies to A in the menom Troonfusion of A to B or B to A, therefore, will go agglutination. Blood types fall into four major groups with respect to the AB antigens A, B AB ad O As shown in Tablo 2 A carries the Actigen od B antibodies B cortes the B mtigen and the A antibodies AB curso both the A and B muligens on the same cell and do antibodies, while o TaWe 2 Human Blood Groups Godtypo Cdation Sobada Hoody LL or L1 LLO LT LL . A D A ad B Note Amo A-D Asta han А B AB n ·Gencs and Man arles Delther antigen and has both antibodies. The group to which o Individual belongs is inherited u a single gene and the difference between In A and a B indtvidual is an allello difference. The tberitance of blood type, the corresponds to the faber bence of a geno that controls the formation of a spodfic antigen. The gene t called the L gene in bodor of the great immunologist, Carl Landsteiner Individuals of type A carry an allcle Lwhich directs the formation of antigen A. Individuals of type B curry a second allelo L' which directs the formation of antigen B Individuals of typo O curty a third allele, Land nelther A rror B antigen is synthestzed. We would aspect to find geno types representing all possible combinations of the three alleles Theo combinations consist of the or different genotypes listed in Table 2 Tho at genotypes glvo four phenotypes, AB AB, end O since L4 and L ure dominant to l but show no dominance with respoct to each other The genetic consequences of this type of inheritance are clear an individual of blood group O might arise from the mating of two to dtvid uali of blood group A (Lc from AO X AO) or from two todividuals, ono A and tho other B (AO X BO) but an todividual of blood group O could not havo o AB parent Converseły en AB individual could not posrbly arise from a moting of two individual of blood group O For this reason, blood grouping is of critical importance to legal pedidoe in bolping polvo such thorny cases us ispues of disputed partntage. While the tabaritance of tho A and B antigens is rodonabły well understood, the pquiring student may wonder how the L gede, whilo determining the formation of i spedito antigen A, at the same Hmo result in the formation af antibodies against B The best Information is that tho association of L and anti-B antibodies to accidental, but the problem is still open. It must be enphastzed that other blood group systeros in man are not wroclated with tho imultaneous prosenco to the sum of antibody to the anogenic product of the alternato alele Other blood traits in man are abo known to be tnherited us an allolic rorles. The Rh factor wu discovered by testing human red cell with anti Stuum produced against red cells of the Rhesus monkey Somo human bloods reacted with these antisetums, others did not revealing that an antigen similar to ono on the monkey cells was present to como human blood cells bu not in others. The antigen wu called the Rheros or Rb factor and it has proved of great interest strice in association has been established botween the Rh factor and bemolytic memta of the newborn Gonetic investigations have revealed many different Rh Jeles, od the tnberltanco of the Rh factor representa a multiple allelic series or a series of very closely linked genes While the Rh factor is an inhalted trait, its relation to hemolytic anemia of the den born is an immunological problem. In matings of an Rh+ father and m Ah- mother stution en ulsofa witch the Rh- mother curries in th+ embryo. You and readly Agrore out the genotypes of tho tad parents required for this sttuatico. In ·Genes and Man some ceka, the Rb factor (aadigen) of the embryo can crots the placenta ad todoco antibody formation to the mother (Since she is Rh- she will ract to the Rh factors who wouki to any other foreigo antigen.) Wo thus havo 1 dtuation in which the Ah factor of the embryo Induce antibodies to the mother and the entlbodia can now retur md dan go tho clayo by uplatinating and destroyfog tho embryo red calls (Fig. 39) Since the total amount of Rh factor in the embryo ts sinal, tho totul Imount of tibody forded in the spother will be limited and where relatively httle effect on the Art bort. With piccoedtog Rh+ pregnaces and continuod fruntadon, tho loved of ot-Rh xatibodies will incrono In the mother s serum, Increuring Doxounts of antibodies and enter tho fetal circulation, od thu fn time can gtve itse to i rovere anemia in the fetus. After fow prognandoa, mtibody loves can becomo dangerowly high and tho Dowborn may require a complote transfuston to prevent death It be clear that knowledgo of Rh compatibility in prospectivo parents is of vital importance. We can then be akart for tho possible apparence of hemolytic anemia for the powborn child. If It door ade, a completo transfusion will avoit life Sul) other entgeno diferences are known for blood, and over in the ABO group now differences are all betag uncovered In fact, human blood constitutos magudioent laboratory for genetic capementation. We have discussed the ballbant tovestigation of human hemoglobin und tho mhaltaneo of blood types and the Rh factor in the years abend, it may well be posible that uito co be made of circulating blood cell at oloo to study problems of cell populations to a mi deniler to thut m which we stody bacterial genetia. Up to now our discuon of genetic has been confined mainly to the traneberion of englo genes and thet alleles and to the relationship of tinglo person to spedfc biochemical reactions. Tho inheritance of DADY charcteristic, however appears to be governed by more than one gene M Racher compatibety (after Sob and Ore) 2 pregosy prinsy Ond manunuotion Normd ront + $+ + 1 Ponting and corredoton and steadrias fornoton of control th or boa e madrul on ondtect the wahofia no ·36 Gonos and Man These include such traits as moscopibility to certain diseases, haight, tho dovelopment of the pervous systern, kto color etc. An extended analysis of multigenic inheritanco is beyond the intention of this book, but, becko of its importance to human genoties, wo will briefly describe Odo coro Sue Color Let us so what would happen if two unlinked genes, each contributing oqually wad to determine the difference between black uldn onlar and white. Let the capital letten Y and Y, stand for the black genel and Vu V. for the white alleles Assuto white and black uro bomozygous for the two gones. A cron between black Y Y, Y,Y, and whito Vives would give tho F. Y y. Yg Intermodiato in color between the parents A cross betwocn F Yuy Yay and white, vy would give threo genotypes and threo phenotypes w.wy = white, Y v Ya the amo FYyyy = tntermodiato between F, and white. The three phenotypes would be in the proportion 112 (Wo have left out the pubscripts in two genotypes since the total number of genes is the determining factor Dot whether it ben allelo of the Art or tho socond gone.) If you work out an F XF crod, you will find the result to be I white, 1 black, and 14 with varying amount of intermediate pigmentation In human akta pigmentation, the genetic difference between yollow black, red, and whito mcludes muny gma Estimates vary for tho total number involved, but the ovidenco potut to at least oght mod probably many more. Apude the number is ten, that they are blinked, and tho conditions stated above pertam. In a mattog between two people both heterozygotic for crory genc, 1 tn abont 1000 of their children would be elther white or black, rare occurrence the other children would bo Intermediate. On the other hand, mating betwoce white and inter modiate could produce no children darker than either parent In this curtillod toalysis of multigenke taheritance, certain amplify ing arrumptions were mado Since a large number of gende govern the tnberitance of skin color vre would poct some of there to be lnbod and thu not able to mako equal contributions. The conclusions we arrived at hovrover will not bo badly distorted. This is affirmed by analysis of mult! geolc traits to plants and animals under conditions of controlled breeding. In this cuapter wo have attempted to present an outline of tho principles of human gonetta. There are other aspects of human gedettes, coch with its unique contributioo to the diversity of genetic mechanlains in man, that we annot desalbo because of space limitations-far ciampla, the transmision of color blindness and hemophilla, which follows e pat ten of sex-tinkedinbalance because the genes responsibto for these tralt ere on the Idromosomo but not on the Y (Note that X3 = female b portually diplold for a ser Holed trait, but TY= make it haploid) The significant thing is that the genetic material of man in its transmision ·Gones and Man and action, b similar to that found to other orgmbms, Wo me thu to cendnghy and that information obtained by study of microorganlams, trisects, plots, and animal will be patient to the folution of tho herod! tary problems of man. Perhaps of greatest taterest to our present convic tion that humo gorrotto telf will make important contributions to the beslo problem of gemoties, a Automent that would have been considered tmpland.blo to yours ago ·Genetic research during the past ten to fifteen years has been engrossed in the identif cation of the material basis of the gene, DVA, and of the mechanism whereby tho gene functions in the living organban. In our description of some of the current research techniques, of the nccess that has been achieved, and the question that arlso with each now lot of Information, curtain amount of bias inevitably has been introduced. Wo havo koplied, at keast by emphasis, that nuclear Inbert ance is the sole mochanism operative in the transmission of heritable traits and that the gene functions by the determina tion of enzyme structure If this be gospel, then it must be reconciled with all the fact of blology Reconcllation is Dot cosy Consider but one crample. Afan Hurts from a fertilized egg call, ono cell Genes whilch divkles mitotically to produce two and cells these divide mitotically to forma four cells and so on up to a few billion Development cells, all generated by mitosis, all with a gono content presumably identical with that of the first cell, tho tygoto. But wc know that these billions of cells are pot Identical in form function and blochan istry they are liver cells, Derve cells, blood celk, eyo colls etc. Diffcrentiation he accuTed We wonder how these dif ferences are created, how the cells tale up their roles in such a precise and ordely fashion. Wo wonder in mort, what it us that regulates and how regula Hon is carried out Is this an additional and aclusive property of the nucleus, or 1 ·Genes and Development 8 At m fnteraction between mders and cytopless, or cytoplum and environment? These are probleme beslo to m understanding of develop Aequired Tralta Meredity has long been thought to bo untquały oboclated with the aucou. Meddal's laws, to effect, deny the fnheritanco of acqutred cher acteristic except fosofar as tho gepes themselves are directly affected. The role of cytrument in betodity has been a albtact of spoculation for many yours. At the turn of the century a great deal of discrico took place about the relattre roles of environment and cellular factoo tn heredity Pooplo werd tward of the pubtlety with which Living formos adapted to thetr environment: the exquisite chinouflage of certain trsects, birds, and Aretho mfmals, the copactty of deoprea atmals to withstand crushing prearures, the cornom vudloty of halutab ta which bacterte were found, to rulfur wells, to ocean bottoms, to the roots of certain plants, in bot pring. Blologlal hfstory in general todicated that better-dapted spo chor opotred for a given anvtrocament Did the environment play e direct robo to this procent by Attrecting a spectic change in the hereditary opperatus of the organer, or wu this caused by random chenge folored by cyfronmental colection! This problem ww put to caparudcntation by the German scientia, Anguunt Wedemann, many yexri ago The tails of u inbred strain of mico Wero removed at birth for a rumber of generations. Fally the mice weto matod ad thetr progeoy Left untouched. The talks of those offspring grow to portaal length. This capertucot b mdmittedly crudo, but at the leart It nuod nome doubt about the tabeltanco of cavtronmentally bducod trilt, e strongly held belief at the time. More dhumattog experiments have recently been done with the help of bacterta and antibiotics If you grow a largo population of E. coll to the laboratory you will goerally And that the population can be destroyed by streptomy tn By growing very large populattons tho presence of streptoorycte, you can obtat population resistant to stropionrychn. The property of those re htunt bacted aro found to be reabstant to streptomycin even when the tontiltotie removed from the growth medium. The question is, de strop tomycha otiso the rabtancesor did it will the sepoltivo bacteria and perput the growth of procrbating redistent bacterta which aroco by mutation for depeodent of the presence of the antibiode? An fogenho esperimeot by Jare Lederbery prorded a solution. Ho dovbed a method to abow that to a loge population of Kensloo bacteria which bad never been a posed to streptomayote, about me to ten million bacteria wus resistant to streptoorrycin. He could pick out this bectertim od let it divide and form. very bore population, and the entire population was feridont to strepia my that without the bacteria ser being exposed to the antibiotic ·90 Gonus and Dovelopment This aperiment, and many others, implies that Hylog thłags, through geno mutation, are andoned with a certain potenttal for adopting to a now cerviroudont if it proves nocorary But this potential to not infinite. Dinosaurs were duplaced by other living forms, poetumably because they could not meet the challenge of changlog tovtramental conditions. The ovidenco today than, suggests that with modom mutedor, plus the end less reshuffing brought about by geno recombination, living forms CD offer a wide variety of response to tho environment. The concept that tho avtronment can Induco a specific heritablo chango is not supported by aperimental data. Russian geneticista, however have raised the problem adow Polital philosophy tn Rogla demands that the enviroment pluy hereditary role for Mendet dogma docroes that social forces we apablo of forgtog filtter race. This doctrino is purported to have received crperimental rupport from the work of Lysenko eod his school, who have attemptod to prove that pormenont hereditary change can be duced in plant by grafting, or in animal and birds by moans of blood transfoston. Numcrow attomptar havo boon mado la other countries to daploato at least tho major experiments on which their conclusions rest, but without ruocen. At tho present time therefore we can only state that Lysentoirm has proven largely nonproductivo in torms of genetic theory. It is essentially rovival of an outmodo gerrotic theory roapplied for political rather the scantiflo purposes. Although apartmental data do Dot support the theory that acquired traits aro bereditarlly transmitted, how do we daarify ach phononena AS bacterial transformation and transduction, for bad we know that now genetic trots aan bo acquired by a microorganism from its surrounding modtam? In these instances, bowover the trelts have been acqutrod by the physlal Incorporation of genetic material, DNA, and thus the mosto nlan diffen frain the older conxcepts of how scquired traits are transmitted. Although we may conclude that traits acquired from the environ mout may seldom becomo permanently transmissible tnits, this does not norwer the question about the uniqueness of the nucleus in tho trungantsson of bereditary information. Are there element in the cell for whoso trasmission the nucleus b insuficient? Cytoplomlc Inheritance There is a rather easy tort for non-nuclear inheritance. In diplold gopoties, wo know that the egg contributor the balk of the cytoplasun to the cell farmed by gametlc fusion. The sperto contributa relatively Wita If thero are olaments in the cytoplasm that requtro the tranimbulon of a cytoplasike element nather than the nodeus, so would gues that much truts would be maternally transmitted. The progray should then sbow only tho maternal trait Alurry Instances of this type of inheritanco are ·Guna and Development boowz. A good amplo ama be readily observed to plaat radegattan, Vologated plants are those that have arous of pale greed, white, a other colons in otherwiso normally groen larves Tho vullegation can be syumerical or It may bo frregular In Mirabilis, the plant commonly alled the four-o clock, the progmy of cross between palo od green plant is pelo or groen depending on the color of the maternal lino Lom if the maternal line is pale, the progeny oro pale, If the maternal Hoo L green, the progery are groen. This is to contradiction to Medallan ge Dotter. Straightforward duced thhaltad.co roqutres that tho progeny of crow between true breeding pale and green planta be tho como rogard le of tho maternal trut The simplest way to count for this type of Inbarltanco is to postulato that a pod-mudou element derved from the maternal plot detantes this tratt, od w And this to be correct Tho cytoplamo ekroents concernod o variegation ure the chloro plasts, the bodies carrying the photosynthetto groot pigment, chlorophyll Tbo tnberitance pattern of verlegation reggests that the theritance of 1 chloroplast dopoods of the transmission of chloroplet Ibell. The data, in fact, indicate that if a plant were to lose it chloroplost, no mudaar dement is provent that can Initiate to do noso formation Chloro plasti, liko gero, an andaryo cautation and a mutunt chloroplet graa Theo to a mutant chloroplast, furt u mutant gantex roproduco mutant gones, This is why variegation is found. It is clour from a study of color mutanta od vedlegation in plants that the cytoplasmdo particulato plament, the chloroplast, represent a cellular constituent that shows antrinuclear to hattance and that the toboltanco of a chloroplast requires at the mord mum tho transmission of a chloroplast Itrolf. Inberita.co of mdom podo 1 pot mfi cicut Wo aloo koor bowever that noclear gece an affoct the chanctor istio of chloroplast. To explore the relationship of goues and forth kutooomon cytoplasmic pertides of this bod, wo will decouts an examplo drawn from another organism. The goneral characteristics of cytoplasmla inberttanco cm bo dauły demonstrated from the brillant studies of Tracy Someborn and his collaborator. Thero tnvestigators have stodied the genetics of the single-celed protozota, Paromatum curelia Paramactan aurdha ta Anal, alliated organism with a normal mitotic vegetative cycle Cytological studkan reveal that u stogo mtoal contains three poolel, wo macrodudar uod two diplotd micronucle. Tbo McTomcleus controls the cell durlog vegetative growth, while the mkonochd aro Coocetoed with pelotte reproduction Serieproduction occurs by coolugation of two animals of opposite coating type (Fig. 40) Contugation foldates a series of muclear changes that can be rem Dutzed us follow. When mattog occurs, the matcouchems didntegrites od the two micronucle auch undergo metost, dastog bich eight haplold bachel are formed Sereo of these ctght paciel distategrate, and the romataing haplold oudeus prouent hech mattor omlinderkoet one ·Mou & -A 60- Metoo kroproco A 40. Reciprocal fertilation Presocrum (after Sonnebora) mtoto division, giving Also to two identical haploid pudd. Ono haplodd nucleus from och antmal is then archanged, resulting in the formation of two adunak, each carrying me haplold nucleus of its own and ono con tributed by its mating partner These two haplold micle fisto to form a diploid nuclau which, in a series of dovelopmental danges gtved leo to naamal animals containing & Macronucleus and two micronuclel. Confugi Hor, therefore, results in the formation of two animals that are genetically Identical boterorygotes, but whose cytoplasms may differ Paramedum b apable of undergolog a second typo of nuclear roorgnization, ane that does not require meting. Under appropriato nutri tonal circumstances Paramecum will undergo autogumy (Fig. 41) In thd's proces, the macOoucou is again lost, and the two micronucle auch undergo netottc division to form dght haploid midel. Again, # to mating, soves of the nude oro lost. The remaining haplold nuclass undergoes a mitotic division. The two baploid nucle then firm to form the diploid mu claus which, in turn, undergoes A reorgmization that reconstitutes a normal animal. The autoguny results in the formation of a genetially homozygous animal. These two different events Lo, confugation and autogamy make Paramecium a remarkably interesing and useful genetic tool Because certain rocas of Paramecium can be other races wbon pret ent together in the sumo culture modium, certain stratos are nld to contado a Wller trut. Struns of Paramecium, therefore, con bo characterized - either Juler of sendtivo types depending on which is the west and which the victim. To determine the genetic basis of this wler truit, ! Autogamy o le modum (after Sonmebort Degeneration of Nous of 958–8–8–6=0 AN ·Genes and Development 93 TO CO Tou a killer and a sositive minel. After conjugation, the animal seperto, tod the phenotypa of the two cell Hoes derived from the two coolagant (eacoafugents) can be determined. Sloco conjugation results in the formation of identical hoterarygotes to would expect that both acontogants should be ethet lillent or sendttves, depending on doxal. nico relationship Surpolsingly however after conjugatton the animal that were killar idi killers, while the animals that were sometimes remain sensities. Tho tratts of the esconfugeab, therefore, are determined by the perental call and persist despite modeer Identity When mimals are per mitted to undergo autogumy od thus form homozygotes, revealing remulta o obtained. If the progeny destved from the sendtivo exconfogunto mdapo utoguy only sensitive animals 210 recovered, but if the progeny of tho heterozygous ble arconfogant ondergo autogamy half the annab tre stopitive and half an bilen. A 11 segregation has takon ploco ut matoguny clearly indicating that a gonotic factor by segregated Autogatny Inheritanco of this tratt xhont certato odd features. Confugation shows no moclear trunkumbakon, but gene sogrogation is seen at autoga muy Lo study of this phenomenon, it was discovered that occasionally billet boda raudtiro enjoy prolonged conjugation and that under these trans sances, although the killer strain remains lilla the senativo trans formed into a killer Upco tatoyunry both cell lines now a 1 l sogresu too for killers and sensitives Conjugation Dormally results on retention of the original tratt, La, Ledlens remata Lillore and sensatte raato sensitives. Prokoaged confugition, bowever permite rendtives to be transformed toto blemu. Wo mow that the difference between pormal pod prolongad con option combo bo escribed to a difference to podlear exchange, but the difference could well reflect a diference in cytoplamic change-tho longer tho conjugation, the more ytopluim achangedIt ww postulated that 2010o clouent to the cytoplast of the billets could be transmitted to teorito enlmal during prolonged comfogation and cause the trantforma then of versiyo to killer This turned out to be true. The killer trutt requtres that a specific chevrent be present to tho cytoplasm. If, during contagution, this element to transmitted from Hier to opatro to the cytoplasm, transformation of sensitive to kuller occurs The fact that escoafugats show a segregation of Millers and send tires poo witogwoy to turo nggests that in order for this cytoplasmic clement to bo functional, the antal must possess a specificanclear gente. Tho cytoplasindo element to alled bappe, end the govo required for its repb attoo, K. 4 Hilor after Autoguny to gooetically KK, the xositta lk. After Dating both sensitive and Hillent pro heterozygous K. In the absence of the cytoplasmlo trapuntation of lapps, which co occur only during prolonged cootigation, xosttir, although getretirati apablo of becoon the Liers, remain seoulthie, doce no Lappe, ble the Where ·94 Genes and Development with kappe present, renata killers. Upon autogamy half the olmal go pocted to bocomo homozygom, KK, and half homozygou, H, the latter group bocoroc sensitives Thero principles wero dartved in the abeenco of vtrual evidence of the presenco of bappa In subsequent experimentation, the prodictions were confirmed. It has been shown that killer entoral do pomens e par Hculato element in their cytoplam and that this alement must be transmiltod if the hiler tralt be to be atublished It has further been confirmed that tho animal must bavo a gene (K) in a spoofto configuration for this dloment to reproduce and act. In the absenco of tho transmission of tho kappe particle, do puclear elenet is present that con tollato the do nooo formation of this particle, The larppa partido, in turn, requires for Its duplication & spodfic genetic constitution of the optimal The Wiler tralt, therefore, bo geno-controlled but not gone-Initiated. The transmeton of lappa to Paramecium reflects the generul che acteristic of cytoplasmic inhertenco Mary particulate elements of the coll show cytoplavnic tberitance, od in each case they show the gen. oral chanzoteristtas found to the inhaltwce of lappe, Len trummbadon requires tremulalon of the partido, but action and/or replication of tho particol coatrolled by the Drucker constitution of the cell Thero traite may in general, be abd to be gono-controlled but not gedo-initiated. This mode of inhaltence seems to be true for the inheritance of chloroplasta, and from tho very fire studia of Borto Ephrust and Pilot Slonimak, It appears that functional mitochondria aro ako mhortted to this way In fact, wo might proport that a large number of the particulato clements of tho cell requtro cytoplannic tramontosion and that if they were lost, no muclour alerents would be provent that could toitiate thate formation. Tho Inhaltrunco of cellule demont auch es mitochoodile, microsomer, etc., however b hard to study stoco cytoplasmic demonta aro prevent to profurlon, and it is experimentelly difficult to creato dtuations to which Do cytoplasmic trimmission of a partido aun take place in any event, studio liko those fast den bed dearly ladikcato that the mudez le port the rodo determinant of bereditary cuncteristics. Nuclear inhaltance is of obrtarts toportance, but tho chanctalsties cell and of a wholo organbon require the transmission and interaction of many elementi Cytoplasmade inheritance has been discussed primarlly from the standpotnt of the transmission of particulato elements. The cytoplasm, bowever may also play a declxivo rolo in determining priorities for geno function In Paramecium aurello & Tracy Sondebarn ud Geoffrey Baulo and their collaborators have shown, auch animal to codowed with a pumber of genes, each of which controls the formation of a specific altlar antgen One mtigon, however is predantoantly formed An entral, therefore, may be capablo of forming andgers A, B C D C bat under specic conditions will form predominantly any B If we crows in animal fonning B antigen with ooe formlag G tho aconfugents and ·Gare and Development 15 ther progody will be geotypically idential In spite of this, tho progeny datved from the Beaconjugant will form antigen B, whereas the progeny dextved from the G will form C Thus an mtigen can be formed by on mnimal If and only if the proper gene present Horover which of the mtiges - be apresed will be detamined by the cytoplasm, and, interestingly cough by the intenction of the cytoplasma with the enviroocat. For fostmct, drastic uhifts to the wytrument, ach a changes to torpanturo and molt concentration, an atto the notion to yothertzo 1 different antigen, but again only one for which tho gepo is prout Thus the cytoplasm plays a doctotro and Intriguing roko in deter mining the alterneto ad achurive priorities to gede functtoning. The nature of the cytoplesunto control to not understood, but, deady the cytoplatan is of importanco in to haltence, and it mobo has many facet. Regulation A rocand problem mentioned at the beginning of this chapter conceras tho uction of all gootie material Does all genetic material act alko and does it detremtoo only the structural characterbithos of product co- Tymes? There bo do dour mower to these questions. We have known for many youry that tho aprostom of sorro tratts is Influenced by other good (modifier genas) Fa bostance, the toteority of pigment foonation in plants can be modified so that you stranu show more pigment formation than others. Then tntenstty differences are gonettaully determatood but tavalve mary gener, auch havtog mall offoct. What do modifier gezes do? They then atves may be genes that cootrol the structure of specifc OnTyte and that secondartly ever accidentally affect or modify tho trait being Deared, or they may be gones or genetio material that regulato tho aproanton of other genes, parhapo turn them on nad off, or change the rate at which they function, od thus differ ther action froco gene that detertoldo entzy po structure. At present, it seems that both hods of effects may adet Forst, lot cumino a pomblo mechanism by which a genocin modify the acttoo of another gene through secondary offects. Alatry cells havo AD Corne, beta-galactonder that by Decessary for the utilization by the call of lactose (Beta-gulectorklase antalyzes the converibon of lactose to glucaso mod gulactose) Alutation of tht geze keeds to lose of activo yo and lots of bilty to atilire lectos to Dos und carbon pource. In order for cell to tako lectore up from the medium, however tho cel bus to form a second curyms, Dlutation the çevo coatrolltog the formation of the optab, miyime (PAW) Loads to loo or lessoned idency in taktog op bacture, Natation of either genie lodependent events, leads to loss of abdity to me Lactose, but for different relook Thus mutation of the upale gone con lead to mod Bantion of lactovo utilization, and fre were not --. nat. L.LT ·36 Gone and Development would doscribe the upteko gerve us a gome modifying the formation of bote-galactosidase. Many genes are known to have toch modtrect effects. The it to abundantly clour that to an organized system, even if all tho genetlo ma terlal wero to act by controlling the formation of specific erymes, gepat of qulte diverso primary function can affect the activity of other genetically determined trults in an ordinary Inheritanco test, genes that arcrta secondary effoct on the trutt under trivestigation appour espertinentally as modifier genes, that is, u genes which alter the predion of the genetic tralt under study Another type of known genotic modification to acmpliBed by som allod muppressor genes, gessor which suppress the phenotypic expronton of other genes. Such genes deed not be linked to the gene thoy affect, and ther action is probably indirect. As en couple, let us Losume that the motel, rinc, tnhibits the action of our favorite enzymo, tase. A mortation resulting in acestvo optuko of doc would lead to appression of the activity thus the geno portaitting zinc uptake would appear to act u suppressor of the t use gono. Liko moodider geres, appressor gmc probably reflect blochemical interactions rather than diversity in the moche Dim of garo action. By now tre have como rufficiently fær to our dosetption of gode . tion to entertain the astoolshing hypothes that all genetic material may not fonction by determining enzymo structure. Recent studia in bacteria soggest that mornio goes do not themselves act by specifytng the structuro of specific onzymes but regulato the sction of other genon that do Thero have been termod regulator gones o distinct from the familiar struc tural genen. Mutation of a regulator gezo con lood to a muted chango in the total amount of enzymo formed by the cell. A regulator gene hos boen found to regulate the formation of tryptophan rynthetese tn Escherichia coll, another good regulates the formation of beta-galactonder to the mmo organism. The rogulator gene fn those auses bave an action which, in effect, turos structural gene on or off Tho limitod ovideoco uvallablo fuggests that regulator genses may act by reprezing czyme formation Entymo represion to crerted via the cytoplasm, but the important fact to that it occun to the absence of protein synthesis. Thus the mocbonton, qoxymo repression, is tbelf DODcuTymatic, and the regulator gepo con trolling repression presumably does not act by itself to form a spedio Forme although it may form a specific roprang RNA Ono regulator gooo au coordinately repress the formation of rovenal functionally related enzyme For instance the gene which regu Later too formation to regulates the formation of other antymas required to the earlier tope of tryptophan blosynthebt. Regulator gener For doccntion of extrmo represion, no D M. Bonoer ad Control Mecha. month Ceile Prooroo (Now York Roneld, 1961) ·Goa and Development which function by Tiymo repression need not be laked to the gener wbox xtion they regulato They are effectivo ored when located on Gother chromosobe, Pesteps of greater interest are operatora geties, geres which require cloro labage for function, genc which may regulato Hrectly at the gave loved without an interventng cytoplasm. Tho concept of operator gones stems from the imaginattro studies of the French wokerto bologist François Jacob, and his collaborators. To see how this taken place, desgrate in activo structul gene nenet itu alebo otho Operator gene u opt and it alelo op The two games are closely Hukod. Two betarorygou diplold comhtuations at pandle op Op Only the second, as comiguration permits orrymo formation. The regole tion by the operator good therefors, requires both Inkage and cu cod figuration These facts and other data obtained by Jacob and with colleagues best that the operator galo cun directly control the formation of the mancing RNA of the structural gene, od operator genes, bko regolator Sebes appour to act bry A mechimbon which does not requtro the operator to foron especific enzyme. One operator gove may control the fociation of several functionally related rozymas, provided tho struktural genes thenaetres aro Ibnikod. For trestance, the poor controlltag tho blowyatbends of hertid too are linked and in all controlled by opo operator Tho gados controlling the formation of beta-gulactoseso nod tho permesso nece Fy for lactone upako are linked in E coli od both are regulatod by thos PANDO Operator gene These observations have led the French workers conto a Don genetic unit, Toperon, which bapacking doul contattas of operator geoo bad the gouen It regulates beto polecaciones opeato P Coottoming resourch is attempttag to define the molecular best of operator S DO Actie Theme bow * ad sem corpo imply that genetic material may bo of two distinct types, one which prexelber the structure of formed O tymo ad Apothes which regulates the ride of eterytoo Carnation Whether the genetic material required for these differlag Winds of gene Action to similar or diferent remains atyptery Regulator and operator Pena, borover tibo stractural rees, oro led on chromowooks, are pablo of recombination, and thus to presumably of DVA constration Hattvo appression of coryme for In sosidentes perto elects, we must keep to mod that the gubyern ·Gones and Development factors Enzymo formation occurs in the cytoplasm and requires the par Hepation of an argenlved biochemical system. Any affect on bne of the componeots of this system (all presumably poder gaetic control) obvlowly cim affect the rate of enzyme formation both directly and fodlrectly In summary we should perhaps simply way that gene expressions rover froo of the genome and that a diversity of interaction clearly occun, as can be seen from the name given to various componenti od their offocts modifier genes, Rupprector gones regulator and operator gener Coutetic rogulatida ts of particular Interest to the field of growth and dovolopment. A single cell, with its entire complement of hereditary to formation, mut interact with its mvironment in a prescribed sequence in Hmo and space to produce the adult orgmism This Ls one of the most compliated events confronting the biologist today In this regard, let us turn for a moment to a consideration of the chromosomal trisomio condidon, Mongolisi Kleinfelders sy ne, etc. described in C? ter & Through Dondisfunction, an entiro dupliato chromosome becomes to corporated into the nudous and creato u abaormal phenotypo Aboormal chromosomal constitutions are known to other Hving forms. In certain plants, normally diploid, duplication of the antiro chromosome Hot Octurs (polyploidy) The resulttog 4N plats reproduce thetr N stato and sean to get along perfectly well, whereas the addition of just one extra chromocomo 's troublesome. The dificulty appears to be one of imbalance. In the haploid, diplold, or polypladd state, in which full complements of chro.co pomes and present, gene products are apparently formed in vurying amounts, but in a balanced condition. An additional chromosome socis to disorganize this situation This is another indication that gene do pot act Independently of ono mother to determining the phonotype of an orgaukam, and that the balance of structure and regulatory genres may well bo critical Among other problems, development poses tho question of orderly genetic rogulation, that I what tists the action of gode on and what turn it off? No satisfactory onwa has been proposed Perhep develop ment requires mutation, since mutation leads to functional differences, but if it does, the mutation must be directod mutation, one that not only shows precision to tons of the genes concerned, but preetsloo with respoct to developmental time. In recent years, the magnificent work of Barban McClintock and R A Brink with corn has covealed genetlo ele monts that an Indoco gerxe mutation and direct the crpresdon of spectic gedetlo material. Even in thb Instance, however tho preddon required for diferentiation is not present. The regulator gonos rod Toperou uro aboo of interest to the problems of development oven if they only furnish hints us to how regulation may be effectod but they too lack the predidlon required by differentiation and development. The cytoplasm bus abo to bo reckoned with In development, for us we discussed in connection with untigenic wlation to Paramedom, the ·Genses and Development 11 cytoplano plan a robo ta determintag the alteroite and accustvo prlarities fi geoo function. Many of the diverse phenomena just discused may actually bo dosely related. From the study of bectarle, we know of colo lar clements that maloy both a chromosomal tod cytoplasmalo odstou.co, for fratroca, lyzogeule phago. Such elemet bevo been tauod oplomes by tho French worken, Freçois Jacob und Eho Wollman. It may we provo true that the elements that can touco gale mutation and direct expresson of specific genetic material in corn, tho regulators of microorgantun, and tho priority-determining capacity of the cytoplasto mry Abully find common ground in cpisodes Once again, wo muut omphasize that althoagh the studies of the past ten years in the field of molecular genetics have been extraordinanly re wuruhy tho information obtained does not provide the solution for many problems to boology particularly those concerning differentiation and developeront It may xol be that genetic donents code whats actions have not yet been described, we dont know At the minimum, dovolop Dent requtras a fol umderstanding of ghetto regulattoo and of the mter Actloos between miclover and cytoplasmic elements Genetics and develop ment constituto a field of tremendous experimental pomodities, a Geld to which towany dow blological lewe aro Holy to be ducor trod in the future ·In the course of the past dety veart, wo bere learned much about heredity and Its underlying chanical basis. In turn, genetlo kaowlodge has contributed to mans we foro on mmy lovels. The material remards to society dartved from such Immovlodge have already been large, and will undoubtedly prove larger in the fti ture. An exciting chapter in gonetto his tory has been written in the production of high yleld strains of hybrid corn, of high-yield wheat trains restant to ut tack by the fimagal panedter, rust and mut, which formerly cutisod padonwide crop fathere, and to the more recent slightly incredible, inre of X-ray sterilizod malo hlow files to help andicate the por tulont Krow worm in the South. There all attest to the value of genetic knowledgo in eliminating pestilence and to brood ing animals, plants, and microorganland to give herdler more productive strafos and to create the world's availablo reource of raw materials, antibiotics, and food. Today « glanco at the Dewspapers, with articles on population arplosions, the drive of Dowly cinerging nations for conomic relf-ruliciency od livo pollo vaccines obtained from mutmt vfros stats, will again remod you of some of the consequences of Popn s curtosdty about the soalled frory tower concepts of the genre, DNA, end dessenger RNA However let us to our attention to mill another topic of contemporary importance, cught up in recurrent omni nous beadlines, to a topic that now on 100 Heredity and Hiroshima ·Heredity and Hiroshima 101 pages the attention of people throughout the world the global godetle problema ping from the hardening and explottetion of atomic energy We know that a portion of tho stupeadows eorgy reased from muclear todon od fudom to released in the form of high-energy tonizing radio How, and in the form of ndioactivo Isotope of elements such a stron them and carbon. Toolzing radiations we highly mutagenic Before the dvent of atomio energy tho known mutagenic agents with which the bundan population bad to contend werd Dot of planning comcom For erampla, ultarviolet Hght hos bow tissue penetrating properties and though it comes burning of sldo and may even induce akto cancer It hos no mecked motagoulc effect on other human cells Chemical agents rock mustard po uro deletalous only when foals deliberately set then bapo to bo buhaled, ond base malogues are ordinarily not present in tho diet, although they may bo used to treat or control vulous crocan. In from, theso ero mutagenk gemts under our control Thoy cam bo used or forgotten ut vil lontong naduation, bomever is a different kettle of fish. Highederty radiation is capablo of deep those penetration and is marstvoły destructive and mutagende Stoce our environment to bombarded by a certain amount of background relation from maturally occurring ridhoactivo okmcuts and from outer space, lonistog radiation to a Dutagen we cannot mattrely Control and agutust which wo dro Dover completely protected Onor presunt concern to with the tacreening mounta spero toto our environment from moclou explosions Each of we now receives moro radlation than did our forefather, and our children may receive mora. Since the background radiation has shot upired to the past twenty yours and stoco bontstag radiation is mutagenis, wo must gtve thoughtful condideration to the pos atblo genetic effects of this increase od of how great o otpoguto the human population can withstand. On concern with loptstag radiation to of two kinds, its effect on tamtal time and recreedtog generations, mod ita effect on matka terre, on . Lot u flyst consider somatic effects theto a pociation betyroci pamato eboormalities, rich a cocer and relation? The fra quency of leukemia, a enci chenstertred by an access formation of white blood cello on bo increased by radiation. In the population of Phoehtona md Nagunk that waytved the atom bombs, there was a metod toorese ta kohemie dostog the sobeqaret Evo yourt. The mano dation betwoce laitoale und radiation to achibited to other groups that have somehow been posed to increased ndiation There is therefore clear relatiomhtp botineco nereddog ubount of radiation and increating fixedesco a ce Wo bow that radiation results fo soowtio pritation. In view of the Correlation found between leukemia and ndiation, does this met Cracer bo protational to origto? Wo do box bxow to bave cope ovidenco that pro entroal leukemias cao bo bodwood by a vtri ·02 Horodity and Hiroshima wo know that interactions between bacterie and bacterial vinoses aro modided by ndiation. We cannot, therefore, conclude that the locToto In leukemie socated with a fncrease to radiation isos * . conso quasca of mutation for tt coald result from tho fnteraction of brradiation, virus, and host. This is perhaps a fair assessment of the relation of india Hon to ancer th getteral. Radiation could induce cancers for a number of different reasons. Since cancers have diverse argins, they may be caused by a viros, a mutation, or other factor Regurdless of the details, box over thero is a socation between on increang amount of radiation mod an increasing incidence of cancer Radiation i deurly a potential Porpatic hazard Wo know of stll other romantic effects of radiation, for & rolationshop between trradiation and aging has been observed. With increasing umounts of radiation, longevity is shortened. In fact, from animal apal ments it appears that the shortening of human kifo may well be mousured to days per tmit doso. Again, increasing radiation must bo viewed as a fomatio hard Uncontrolled release of nuclear energy uso toparlls tho human population because it cousa the abundanco of certain radloectivo oloments For instance, medioactive strontium 90 farmed as a consequence of hydrogen-bomb aplosions is extremely dangerous, since it has a long half ufo und cho replace cultum in bone. It is carried into the looosphero and L ultimately wusbed down and widely deposited over the earth, surface by run and now from tho soil, stronttom 90 is absorbed by growing plants, the plants aro ingested by attie, and strontium 80 appear ho milk and milk product. When taken into the body this radioactivo teotopo can take the place of culturn to the bono timue, particularly to grow tog children. Strontium 90 to bone constitutos small centers of radioactivity and, If present in muffictent amount, an give rise to booo Uncer and an ety of other abnormalities. This is truly a new cyclo of nature a twentiethcentury cycle. The unount of strontium 90 has already been markodly Increased by nuclear emplostons, and we have no clear-cut anrien to how much strontura 90 can be safely tolerated in the bumen det or how big up togauso in the total amount of trootfunn 90 an be absorbed with out adverse effect on the population as a whole Safety lovels to man are difficult to determine They require loog tert study but our restless world denies tis timo. Decisions affecttog the biso of nuclear coetgy must be made, but unfortunately our information about the deleterious effect to modo per unit treronse of radiation to foedoquate to perralt us to offer unequivocal biological advice. The thought ful person must agree that 10 Increuse lo radiation is attendent with hamad, od that wory political decision loading to Increase lo radiation must bo made on the basis of the garest, most soul.searchilog conddere tr A second problen posed by bomb testing to the effect of lontzlog ·Harodity and H roghana 1 OF nadation on germinal tissue. There is no question that arutattoo nta doo chanced by madla Hon. This was shown yters ago by EL J Muller with Intyr od Drosophila By for the great maputty of such mutations to Lethal or doletcrioul. As background radiation Dress, te svetago doro toetved by eart of us tocrosses, and presinably the total mumber of mutations present to ar gumot olla niso tacente. If the total member of transculablo mutant goes is on the tocross the trumber of one harmg deleterious developmental effect obviously mist abo stac. For tho Relo of faturo generations, we desperately need information co boor bug un tocroto to the genetic bude , buman population Cho wirtustand mod furtvol In the populations of the cities of Atroshima and Nugaald that Furvived the atom borph, despite the observed incrouro in frequency of bonbora, no rabstantial neo to tho frequency of spontaneous abortions or to the number of still born infmts hus born ooted. There finding, though foregroentary and of Interest, once the rate of spontaneous abortions and Alberthu partape should provido como cloo about the bacreso to down ant mutant lothal geoes to the fridbated population, ad tho tocTouto the dominant Lethulo in turn might alvo at boost a rough cothmato of the Aprobo ta tocentro lottial geots. But do In TELO we found Perhaps davrant lothals ta luunnans eto nuro compared to recenstvo lothes, or pertapa dominant botheb a quictly filtered out by cell death. Inbreeding apartments are nocetuary to answer this point, but rich expertment pro donlod v Mimy Endiroot methods bave been wood to estimate the palled gezette load (number of rocontre lethal and deletartom genes arried the human population) Analysis of the vital statisthes of various shall population in which consangut cow mentego bave occurred for many Inerations permite a rough estimats of groetic boed. The estimates baro Tuled, but ta çoneral they have todicated walker lowed that would have been noticipated from studies of other organiom. For example, reattely burgo numbers of rocesetve lethals auo wamalato od bo maintxoed in buboratory population of Drosophile, with a constaquoat redaction to the Thality of the population when to brod. La bantne populations, the number of rocerstvo lethal appears to be relatively anal it must be emphasted that the data ou bram popole Hong Kro fow and the math to uncertain. However it is posible that Lethal do not meumalate in me, but are tentouted within the fint for divtalous of the fertiltrede. If the fa truke od Of tho dare obtained from the Nepal and Atohtore populations illustrato what we can aspect in hura populations, then the widence suggest that an ice to radi to may coaptttuto a greater moestic than grminal board but tredia tion and its affect on the genetie lord of the burden population roman htuul umbnorma One lact does remalo crystal clear [ocreusod nasom ropresents a ·D4 Heredity and Hiroshima malou human hezard, a hazard of recent adigin md 000 that must be stodied in detall. In the absence of overriding political considerations, backgroumd radiation obviously should not be caused without a pounder knowledgo of the biological coosequences of such an increase. How can moro detalled information about the effects of radiation on human popule tions bo obtainod? Tho answer in part, must come froon population studies of other organisms, and it also hinges on how accessful we are in securing detallod Information about the genetks of man. As mentioned earlier techniques and bow being doveloped that to thmo may cablo us to grow differentiatod cells to Histio culture, and we may soon bo able to mody differentiated human cells much as we now grow and audy bacterial cells. Partaps tho methods that hava proven fruitful to defining genetto peche ntoms in microorganisms will then prove fruitful in defining genetic prob bers to man, Including the effects of radiation. The problems are mmodiato ed urgent md ro the thoughtful attention of all of us. All of heredity cannot bo presented in the alim volume. Wo havo attempted to prevent the current idou on the cheonical basis of beredity and its mochanisms of action in the livtog cell In addition, we have do albed some of the latest trends to genetic research, tho problems that confront and the expectations that stimulato im. To do this, we have touched but lightly on the contributtoos of the glont of the past. And wo havo omittod, or metroly hintod at, many other Bolds of genetic Inquiry that are bustling and productive. If we have acceded in whetting your appetite, wo laavo it to your curlosity to explore moro deoply into the Kolonce of genetics. In our own blused opinion, to think that the futuro of genetia con bo simply stated by these lines from poorn by co. Cummming -Histon there hall of good ontvorm dat door lato go

·Selected Kerdags
There are my escollant text of gomul proti Werofer to but
two of the od ono coloction of oplo peponi.
Stmot, E W L C Dumn, and Th. Dobyhandy Proactola of Canetih
Bth od. Now York: More -HIST, 1858.
Srtu, AM, and fry D Or Coral Genetian San Francisco Froman,
1038.
Patern, Juroco A, od, Clank Paper to contar. Englewood Chil, NJ
Preuther, 1950
CHAITU I
Swoica, CP Cytolog and Crognation. Engorood life, NJ
Priatico-HAL, 1957
CHAITU 2
Hotchklos, Ralita Dood Ente Won Trap formed Bactering Soon
fic America, 195 (November 1950) 186
HTU )
Boule G W Cow ad the Choroby the Orain Science b
Progress Site ores. Now Hots. Yale Untreruty Press, 2017
1
SHAFTA 4
Aninaan, G. B I The Holeculer Basie of Ecordion New York Wiley
IOS

·0% Selected Readings CHAPTER 5 Brenner on the Impoodhality of AD Ovar lapping Triplet Code in Information Tranfer from Nucleic Acid to Protet, Procardiga of the National Academy of Sokonca, Washington, 43 (18571, 687 Merobon, M. ad F W Stahl, "The roplication of DNA fn Escherichia coll" Proctading of the National Academy of Science, Washing ton, 38 (1958) 053 CHANTE Benzer Soymour. "Tho Fanontary Votte of Horodity to W D Microy and B Glen, odo, The Chemical Beds of Heredity Baltoro Johns Hopkins Unternty Press, 1958 Bandar DM, Y Suryam, and J . Dolor Ceactio Foo Structura and Enrymo formation, Pedmetion Proceeding, 10 (1980) 820. CHAJTER 7 Wollman, Ebe, and Francois Jacob "Struality in Bectorle, Scandic American, 185 (July 1858) 109 Zinder Norton O "Transduction to Bactan, Scientific America, 199 (November 1858) 3& CHAPTER Hanth, Hupen Blochemical Constich Now York Cambridge Unt Varitty Phon, 1900 CHAPTER 7 Beak, C., The Coatics of Poarecun aurelio. New York Cambridge Untversity Press, 1854 Jacob, Fricots, P Scbeoffa od Elbo Wallmu, Episomic Elements to Bacteris, aftcrabtal Constien, 10th Symposed of the Society for Good Microbiology Now York Cambridge University Press 1900 CHATE 10 Boodlo, Coorpe W Tonting Raduatlon od the Citizen, Scientific Amrit am 201 (Sopterpber 1999) 319 Kniphoe Edward F, Tbo Endioath of the Screw-worm Fly Scket Hac Aserico, 2003 (October 1980) BL.

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·0 Index F Fine Atrocton, 57 Flapoptothe 30 Fate roootyper, 04 Codes, 47 comm, 48 overlapping. 47 Complasentation, 00 map , 61 Comungunity 78 Coordinato logradon, 08 Copy-choke, S. 58 CRY, detection, & Tu, B4 Crong ova 21, 84 Cromover froquacy 24, 73 Cryptophy 47 Cytoplace the tunes, 80 chloroplast, OI mottochondrio Cytomboc, 41 Gelectorem, 40 Gamer, Goog, 15 bochemical reactions to 18 definition of, A Etymo ad, de od 75 rutrition und, 84 Geactic tmbulance, 88 bud, 103 region controlling to formation, Crowtb od dortlopot, ba Countdo, 41 D H Deletion, 50 51 Derty pracht, Dictionary 47 DXfferontation, 89 Diploid, 4 Diplondy 07 Dronne Kocopullity DNK, & 41 Ampould code of 40 hybnd, u putover 40 mptation of u pnghtroded 40 synthews of, 40 structure of, 42 Wattoo-Cret model of 43 Dantonce, Drosoplale 73 rant chrumme o, 4 Holold, 4 Hemoglbta, 81 Hogerpretation of, Hemolythe Locml, 84 Heredity 1 the material beal af, Hoturocarron, 81 Hetorary poes, 64 Hfr 09 Hotazy poca, 04 Human cytology 70 Hybrid conn, 100 Indoke tycerdd pboophata, 31 lobortuoco tort, 15 London, 51 Inredlatka kod uglok 100 E K Lupp, 83 Kiley tratt, 22 Klepfeder Syndrome TT Envtrument, bo Ema, atalytic attes on, 37 pitory structure of 87 I prodon 0,80 three locudonal tructure of 37 Ephronics 09 Escherichia colt, es Eurolugents, 99 L Leului, 101 bios, 20, 71 ·Indo 11 Loked foods, 20 L, 81 Lapton, 07 Labom, 90 mpy 00 Nacker aplodon, 101 Nocleod, 1 Nutritional th, 35 O M Ono pone, opetarym bypotb. 29 Operator rog, 07 Drotthon, P Wor, 77 loodusfonction to 77 * detination to, 77 Happlag, 24 Hatte typer, 10, 78 Kated, 8 Med RNA, Weronome, 3 Mitochondria, & Wito, 4 Madah pames, 85 Hoepben, 78 Hukiple alleles, B3 Houston, 84 protu, 14 ba ambao mold once. 38 muy tractor, 34 frequency of, 24 cone, 50 Dan 48,60 polat, 50 mun, 50 Mudathio ad cloction, otthool d, 88 Ponnection, 01 Is code of, 91 prolonged cooperation is 03 Portal betreypotas, Permouc, AS Phenotype, OS Pheorylaantoe, metabobo of 78 Peoyotoduri, 78 tabenama of 7 metal repubweat, 70 Proteto, 8 00 enrymas, DS synthesis to Liro, 63 ) O Questhettre aproban, 97 R Moto, 57 58 Myoglobin, 59 N N144 Necrosport, 10, 17 coupon... 17 Peton 101 bnpork 100 Random utotorcot, 10 Race re, as Reccone lethel poet, 105 Recombombo 1054 beton 57 wab , 57 Roon, J7 . Kedacth drogo Rektos 03 Rapolator popes, Replatton 44 ith acto 14 RYA, 64 in ropor arden & Couto de Werthe, 13 , 17 Cold, 10 tabertoa tek , 17 W cycle of 10 The tyres of 17 Koton of 77 Not Three The One 70 Netros sod, 61 S Condstoction to control deere 70 to huo, Wm-tomma leur tsborttee 90 She is a Skree

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