遗传学的基本原理课件

2022/12/21Thebasicprinciplesofinheritance1Chapter3

Mendelism:

TheBasicPrinciplesofinheritance2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance2ChapterOutlineMendel’sstudyofheredityApplicationofMendel’sprinciplesFormulatingandtestinggenetichypothesis(遗传学假说的形成和检验)Mendelianprinciplesinhumangenetics(人类遗传学中的孟德尔原理)2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance3TheBirthofGenetics:AScientificRevolutionPisumsativumThesubjectofGregorMendel’sexperiments.2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance4Section1

Mendel’sStudyofHeredityGregorMendel’sexperimentswithpeaselucidatedhowtraitsareinherited.2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance51Mendel’sLifeStory1822-18842022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance62Mendel’sExperimentalOrganism,theGardenPeaThegardenpea,Pisumsativum,isadicot(双子叶)andatrue-breeding(纯种).Onepeculiarityofpeareproductionisthatthepetalsofflowerclosedowntightly,preventingpollengrainsfromenteringorleaving.2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance73MonohybridCrosses:thePrinciplesofDominanceandSegregation2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance8柱头雌蕊花药雄蕊去势的2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance92022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance10Mendelinferredthatthesehybridscarriedalatentgeneticfactorfordwarfness,onethatwasmaskedbytheexpressionofanotherfactorfortallness.Clearly,thehybridsthathehadmadebycrossingtallanddwarfvarietieshadtheabilitytoproducedwarfprogenyeventhroughtheythemselvesweretall.2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance11Hesaidthelatentfactorwasrecessive(隐性)andthattheexpressedfactorwasdominant(显性).Theserecessiveanddominantfactorsseparatedfromeachotherwhenthehybridplantsreproduced.Thisenabletoexplainthereappearanceofthedwarfcharacteristicinthenextgeneration.2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance12Thesefactorsarenowcalledgenes;theirdominantandrecessivearecalledalleles.Allelesarealternateformsofagene.Genescomeinpairs.Eachofparentalstrainscarriedtwoidenticalcopiesofagene—inmodernterminology,theyarediploidandhomozygous(纯合子).2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance13Duringtheproductionofgametes,thesetwocopiesarereducedtoone;thatis,thegametesthatemergefrommeiosiscarryasinglecopyofagene—inmodernterminology,theyarehaploid.Diploidgenenumberwouldberestoredwhenspermandeggunitetoformazygote.2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance14Ifthespermandeggcamefromgeneticallydifferentplants,thehybridzygotewouldinherittwodifferentalleles,onefromthemotherandonefromthefather.Suchanoffspringissaidtobeheterozygous.Thedifferentallelesthatarepresentinheterozygotemustcoexisteventhroughoneisdominantandtheotherrecessive,andthateachofthesealleleswouldhaveanequalchanceofenteringagametewhentheheterozygotereproduces.2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance15Furthermore,randomfertilizationswithamixedpopulationofgametes—halfcarryingthedominantalleleandhalfcarryingtherecessiveallele—wouldproducesomezygotesinwhichbothalleleswererecessive,Thus,wecouldexplainthereappearancetherecessivecharacteristicintheprogenyofthehybridplants.2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance16Mendelusedsymbolstopresentthehereditaryfactorsthathepostulated—amethodologicalbreakthrough.这是一个创举2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance17Thegenotypeisthegeneticconstitutionofacell,anorganism,oranindividual(i.e.thespecificallelemakeupoftheindividual)usuallywithreferencetoaspecificcharacterunderconsideration

基因型是一个细胞、一个生物或一个个体的遗传构成形式(比如组成个体的特定等位基因)，通常与其控制的特殊性状相关。2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance18Aphenotypeisanyobservablecharacteristicortraitofanorganism:suchasitsmorphology,development,biochemicalorphysiologicalproperties,orbehavior.表型是一个生物可以被观察到的特征或性状：如形态、发育、生化或生理学的性质或行为。Phenotypesresultfromtheexpressionofanorganism'sgenesaswellastheinfluenceofenvironmentalfactorsandpossibleinteractionsbetweenthetwo.

2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance19Theallelefordwarfness,beingrecessive,issymbolizedbyalowercaseletter

d;theallelefortallness,beingdominant,issymbolizedbythecorrespondinguppercaseletter

D.Astheparentalstrain,thetallanddwarfpeaplantsformthePgenerationoftheexperiment.Theirhybridprogenyarereferredtoasthefirst

filial(子女)

generation,or

F1.2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance20Uponself-fertilization,thetwokindsofgametesproducedbyheterozygotescanuniteinallpossibleways.Thus,theyproducefourkindsofzygotes:

DD,Dd,dD,anddd.However,becauseofdominance,threeofthegenotypeshavethesamephenotype.Thus,innextgeneration,calledtheF2,theplantsareeithertallordwarf,inratioof3:1.2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance21Whichresultswouldhappenwhendidthisanalysisonestepfurthertake?TheF2plantswereself-fertilizedtoproduceanF3.AllthedwarfF2plantsproduceonlydwarfoffspring,demonstratingthattheywerehomozygousforthedallele,butthetallF2plantscomprisedtwocategories.Approximately1/3ofthemproducedonlytalloffspring,whereastheother2/3producedamixtureoftallanddwarfoffspring.2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance22Mendelconcluded:Thethirdthatweretrue-breedingwereDDhomozygotesandthatthetwo-thirdsthatweresegregatingwereDdheterozygotes.Theseproportions,1/3and2/3,wereexactlywhathisanalysispredictedbecause,amongthetallF2plants,theDDandDdgenotypesoccurinaratioof1:2.2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance23MendeldiscoveredtwokeyprinciplesThePrincipleofDominance:

Inaheterozygote,oneallelemayconcealthepresenceofanother.Thisprincipleisastatementaboutgeneticfunction.Someallelesevidentlycontrolthephenotypeevenwhentheyarepresentinasinglecopy.2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance24ThePrincipleofSegregation:

Inaheterozygote,twodifferentallelessegregatefromeachotherduringtheformationofgametes.Thisprincipleisastatementaboutgenetictransmission.Analleleistransmittedfaithfullytothenextgeneration,evenifitwaspresentwithadifferentalleleinaheterozygote.原理2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance254.DihybridCrosses:thePrincipleofIndependentAssortment2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance262022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance27Yellow,round 9/16Yellow,wrinkled 3/16Green,round 3/16Green,wrinkled 1/162022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance28Thisanalysisispredicatedontwoassumptions(以2个假设为基础):eachgenesegregatesitsalleles,andthesesegregationsareindependentofeachother.Thesecondassumptionimpliesthatthereisnoconnectionorlinkagebetweenthesegregationeventsofthetwogenes.Forexample,agametethatreceivesWthroughthesegregationofthetexturegeneisjustaslikelytoreceiveGasitistoreceivegthroughthesegregationofthecolorgene.2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance29Dotheexperimentaldatafitwiththepredictionsofouranalysis?2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance30Mendelconductedsimilarexperimentswithothercombinationsoftraitsandineachcaseobservedthatthegenessegregatedindependently.Theseresultsofthesesexperimentsledhimtoathirdkeyprinciple:ThePrincipleofIndependentAssortment:

Theallelesofdifferentgenessegregate,oraswesometimessay,assort,independentlyofeachother.

2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance31KeyPointsMendelstudiedtheinheritanceofsevendifferenttraitsingardenpeas,eachtraitbeingcontrolledbyadifferentgene.Mendel’sresearchledhimtoformulatethreeprinciplesofinheritance:

⑴theallelesofageneareeitherdominantorrecessive,⑵differentallelesofagenesegregatefromeachotherduringtheformationofgametes,and⑶theallelesofdifferentgenesassortindependently.2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance32ApplicationsofMendel’sPrinciplesMendel’sprinciplescanbeusedtopredicttheoutcomesofcrossesbetweendifferentstrainsoforganisms.Section32022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance33Ifthegeneticbasisofastraitisknown,Mendel’sprinciplescanbeusedtopredicttheoutcomeofcrosses.Therearethreegeneralprocedures,tworelyingonthesystematicenumerationofallthezygoticgenotypesorphenotypesandonerelyingonmathematicalinsight.2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance341ThePunnettSquareMethod(1875-1967)BritishGeneticistIntercrosse互交2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance352TheForked-LineMethodTheforked-linemethodforpredictingtheoutcomeofanintercrossinvolvingthreeindependentlyassortinggenesinpeas.2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance36Theforked-linemethodforpredictingtheoutcomeofatestcrossinvolvingthreeindependentlyassortinggenesinpeas.2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance373TheProbabilityMethodAnintercrossshowingtheprobabilitymethodinthecontextofaPunnettsquare.2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance38Applicationoftheprobabilitymethodtoanintercrossinvolvingtwogenes.2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance39KeyPointTheoutcomeofacrosscanbepredictedbythesystematicenumerationofgenotypesusingaPunnettsquare.Whenmorethantwogenesareinvolved,theforked-lineorprobabilitymethodisusedtopredicttheoutcomeofacross.2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance40Section4

FormulatingandTestingGeneticHypothesesThechi-squaretestisasimplewayofevaluatingwhetherthepredictionsofagenetichypothesisagreewithdatafromanexperiment.2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance41Awell-formulatedscientificideaiscalledahypothesis.Datacollectedfromobservationsorfromexperimentationenablescientiststotesthypothesis—thatis,todetermineifaparticularhypothesisshouldbeacceptedorrejected.2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance42Snapdragons,Antirrhinummajus(金鱼草)Dothiscolordifferenceshaveageneticbasis?2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance43Wecouldhypothesizethatflowercoloriscontrolledbyasinglegenewithtwoalleles,W(forred)andw(forwhite),andthattheflowersofWwheterozygotesarepinkbecausetheallelesarenotstrictlyeitherdominantorrecessive.Accordingtothishypothesis,thePgenerationwouldbeWW(red)Xww(white),producingF1hybridsthatwouldbeWw(pink),whichwhenintercrossed,wouldyieldWW(red),Ww(pink),andww(whiter)F2progenyina1:2:1ratio.2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance44Theactualnumbersseemtobearthisout,givingcredencetothehypothesis.Wemayaskwhetherdatareallydosupportaparticularhypothesis.Thisquestioniscritical,sincethevalueofahypothesisdependsonitsabilitytoexplainthedata.Ahypothesisthatdoesnotfitneedstobemodifiedordiscardedaltogetherinfavorofsomethingbetter.2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance453TheChi-SquareTest(卡方检验)2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance46ComparisonoftheobservedandexpectedresultsandcalculationofX2

foranintercrosswithhybridsnapdragons.2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance47Thedegreeoffreedom(自由度)Criticalvalue(可信区间)2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance48KeyPointsThechi-squarestatisticiscalculatedasX2=(observednumber–expectednumber)2/expectednumber,withthesumcomputedoverallcategoriescomprisingthedata.Eachchi-squarestatisticisassociatedwithanindex,thedegreeoffreedom,whichisequaltothenumberofdatacategoriesminusone.2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance49Section5

MendelianPrinciples

inHumanGeneticsMendel’sprinciplescanbeappliedtostudytheinheritanceoftraitsinhumans.2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance50显性：软骨发育不全、短指、先天性夜盲、皮肤弹性过度综合征、Huntington氏病、马凡氏综合症、神经纤维瘤、苯硫脲尝味试验、克夫相、羊毛状发隐性：白化病、尿黑酸症、共济失调毛细血管扩张、囊性纤维瘤、杜氏肌无力、半乳糖血症、糖原存储症、苯丙酸尿症、链状细胞贫血、Tay-Sachs病等2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance51Thisiswidowspeak!这是一个长寿的显性表型？中国人的美人尖！2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance521Pedigrees(家系)Pedigreesarediagramsthatshowtherelationshipsamongthemembersofafamily.Pedigreeconventions2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance53Whichisdominance?Whichisrecessive?2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance542MendelianSegregationinHumanFamiliesInhumanbeings,thenumberofchildrenproducedbyacoupleistypicallysmall.TodayinChina,onechildonefamily!InUSA,theaverageisaroundtwo!Indevelopingcountries,itissixtoseven!SuchnumbersprovidenothingclosetothestatisticalpowerthatMendelhadinhisexperimentswithpeas.2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance55Consequently,phenotypicratiosinhumanfamiliesoftendeviatesignificantlyfromtheirMendelianexpectationAsanexample,letusconsideracouplewhoareeachheterozygousforarecessiveallelethat,inhomozygouscondition,causescysticfibrosis(囊性纤维瘤).Ifthecoupleweretohavefourchildren,wouldweexpectexactlythreetobeunaffectedandonetobeaffectedbycysticfibrosis?2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance56Theanswerisno.Althoughthisispossibleoutcome,itisnotonlyone.Thereare,infact,fivedistinctpossibilities:Fourunaffected,noneaffected.Threeunaffected,oneaffected.Twounaffected,twoaffected.Oneunaffected,threeaffected.Noneunaffected,fouraffected.2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance57Intuitively,thesecondoutcomeseemstobethemostlikely,sinceitconformstoMendel’s3:1ratio.Wecancalculatetheprobabilityofthisoutcome,andeachoftheothers,byusingMendel’sprinciplesandbytreatingeachbirthasanindependentevent.2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance582022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance594GeneticCounseling(遗传咨询)2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance60Pedigreeshowingtheinheritanceofhereditarynonpolypoidcolorectalcancer.2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance61Inthisexamplethechildrenfallintotwopossiblephenotypicclasses.Becausethereareonlytwoclasses,theprobabilitiesassociatedwiththevariousoutcomesarecalledbinomialprobabilities(二项可能性).2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance62ACunaIndianchildfromPanamawithAlbinismPedigreeshowingtheinheritanceofalbinismPunnettsquareshowingthatamongoffspringwithoutalbinism,thefrequencyofheterozygotesis2/3.？2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance63Insummary,theriskthatTwillbeaa=[ProbabilitythatRisAa]X[ProbabilitythatRtransmitsa,assumingthatRisAa]=(2/3)X(1/2)=(1/3)2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance64KeyPointsPedigreesareusedtoidentifydominantandrecessivetraitsinhumanfamilies.Theanalysisofpedigreesallowsgeneticcounselorstoassesstheriskthatanindividualwillinheritaparticulartrait.2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance65玉米粒的颜色和转基因无关我的博客/home.php?mod=space&uid=616948&view=zdqiao

2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance66Chapter3

Mendelism:

TheBasicPrinciplesofinheritance2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance67ChapterOutlineMendel’sstudyofheredityApplicationofMendel’sprinciplesFormulatingandtestinggenetichypothesis(遗传学假说的形成和检验)Mendelianprinciplesinhumangenetics(人类遗传学中的孟德尔原理)2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance68TheBirthofGenetics:AScientificRevolutionPisumsativumThesubjectofGregorMendel’sexperiments.2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance69Section1

Mendel’sStudyofHeredityGregorMendel’sexperimentswithpeaselucidatedhowtraitsareinherited.2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance701Mendel’sLifeStory1822-18842022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance712Mendel’sExperimentalOrganism,theGardenPeaThegardenpea,Pisumsativum,isadicot(双子叶)andatrue-breeding(纯种).Onepeculiarityofpeareproductionisthatthepetalsofflowerclosedowntightly,preventingpollengrainsfromenteringorleaving.2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance723MonohybridCrosses:thePrinciplesofDominanceandSegregation2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance73柱头雌蕊花药雄蕊去势的2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance742022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance75Mendelinferredthatthesehybridscarriedalatentgeneticfactorfordwarfness,onethatwasmaskedbytheexpressionofanotherfactorfortallness.Clearly,thehybridsthathehadmadebycrossingtallanddwarfvarietieshadtheabilitytoproducedwarfprogenyeventhroughtheythemselvesweretall.2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance76Hesaidthelatentfactorwasrecessive(隐性)andthattheexpressedfactorwasdominant(显性).Theserecessiveanddominantfactorsseparatedfromeachotherwhenthehybridplantsreproduced.Thisenabletoexplainthereappearanceofthedwarfcharacteristicinthenextgeneration.2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance77Thesefactorsarenowcalledgenes;theirdominantandrecessivearecalledalleles.Allelesarealternateformsofagene.Genescomeinpairs.Eachofparentalstrainscarriedtwoidenticalcopiesofagene—inmodernterminology,theyarediploidandhomozygous(纯合子).2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance78Duringtheproductionofgametes,thesetwocopiesarereducedtoone;thatis,thegametesthatemergefrommeiosiscarryasinglecopyofagene—inmodernterminology,theyarehaploid.Diploidgenenumberwouldberestoredwhenspermandeggunitetoformazygote.2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance79Ifthespermandeggcamefromgeneticallydifferentplants,thehybridzygotewouldinherittwodifferentalleles,onefromthemotherandonefromthefather.Suchanoffspringissaidtobeheterozygous.Thedifferentallelesthatarepresentinheterozygotemustcoexisteventhroughoneisdominantandtheotherrecessive,andthateachofthesealleleswouldhaveanequalchanceofenteringagametewhentheheterozygotereproduces.2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance80Furthermore,randomfertilizationswithamixedpopulationofgametes—halfcarryingthedominantalleleandhalfcarryingtherecessiveallele—wouldproducesomezygotesinwhichbothalleleswererecessive,Thus,wecouldexplainthereappearancetherecessivecharacteristicintheprogenyofthehybridplants.2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance81Mendelusedsymbolstopresentthehereditaryfactorsthathepostulated—amethodologicalbreakthrough.这是一个创举2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance82Thegenotypeisthegeneticconstitutionofacell,anorganism,oranindividual(i.e.thespecificallelemakeupoftheindividual)usuallywithreferencetoaspecificcharacterunderconsideration

基因型是一个细胞、一个生物或一个个体的遗传构成形式(比如组成个体的特定等位基因)，通常与其控制的特殊性状相关。2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance83Aphenotypeisanyobservablecharacteristicortraitofanorganism:suchasitsmorphology,development,biochemicalorphysiologicalproperties,orbehavior.表型是一个生物可以被观察到的特征或性状：如形态、发育、生化或生理学的性质或行为。Phenotypesresultfromtheexpressionofanorganism'sgenesaswellastheinfluenceofenvironmentalfactorsandpossibleinteractionsbetweenthetwo.

2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance84Theallelefordwarfness,beingrecessive,issymbolizedbyalowercaseletter

d;theallelefortallness,beingdominant,issymbolizedbythecorrespondinguppercaseletter

D.Astheparentalstrain,thetallanddwarfpeaplantsformthePgenerationoftheexperiment.Theirhybridprogenyarereferredtoasthefirst

filial(子女)

generation,or

F1.2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance85Uponself-fertilization,thetwokindsofgametesproducedbyheterozygotescanuniteinallpossibleways.Thus,theyproducefourkindsofzygotes:

DD,Dd,dD,anddd.However,becauseofdominance,threeofthegenotypeshavethesamephenotype.Thus,innextgeneration,calledtheF2,theplantsareeithertallordwarf,inratioof3:1.2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance86Whichresultswouldhappenwhendidthisanalysisonestepfurthertake?TheF2plantswereself-fertilizedtoproduceanF3.AllthedwarfF2plantsproduceonlydwarfoffspring,demonstratingthattheywerehomozygousforthedallele,butthetallF2plantscomprisedtwocategories.Approximately1/3ofthemproducedonlytalloffspring,whereastheother2/3producedamixtureoftallanddwarfoffspring.2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance87Mendelconcluded:Thethirdthatweretrue-breedingwereDDhomozygotesandthatthetwo-thirdsthatweresegregatingwereDdheterozygotes.Theseproportions,1/3and2/3,wereexactlywhathisanalysispredictedbecause,amongthetallF2plants,theDDandDdgenotypesoccurinaratioof1:2.2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance88MendeldiscoveredtwokeyprinciplesThePrincipleofDominance:

Inaheterozygote,oneallelemayconcealthepresenceofanother.Thisprincipleisastatementaboutgeneticfunction.Someallelesevidentlycontrolthephenotypeevenwhentheyarepresentinasinglecopy.2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance89ThePrincipleofSegregation:

Inaheterozygote,twodifferentallelessegregatefromeachotherduringtheformationofgametes.Thisprincipleisastatementaboutgenetictransmission.Analleleistransmittedfaithfullytothenextgeneration,evenifitwaspresentwithadifferentalleleinaheterozygote.原理2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance904.DihybridCrosses:thePrincipleofIndependentAssortment2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance912022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance92Yellow,round 9/16Yellow,wrinkled 3/16Green,round 3/16Green,wrinkled 1/162022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance93Thisanalysisispredicatedontwoassumptions(以2个假设为基础):eachgenesegregatesitsalleles,andthesesegregationsareindependentofeachother.Thesecondassumptionimpliesthatthereisnoconnectionorlinkagebetweenthesegregationeventsofthetwogenes.Forexample,agametethatreceivesWthroughthesegregationofthetexturegeneisjustaslikelytoreceiveGasitistoreceivegthroughthesegregationofthecolorgene.2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance94Dotheexperimentaldatafitwiththepredictionsofouranalysis?2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance95Mendelconductedsimilarexperimentswithothercombinationsoftraitsandineachcaseobservedthatthegenessegregatedindependently.Theseresultsofthesesexperimentsledhimtoathirdkeyprinciple:ThePrincipleofIndependentAssortment:

Theallelesofdifferentgenessegregate,oraswesometimessay,assort,independentlyof