遺傳學(xué)的基本原理課件

2022/12/21Thebasicprinciplesofinheritance1Chapter3

Mendelism:

TheBasicPrinciplesofinheritance2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance2ChapterOutlineMendel’sstudyofheredityApplicationofMendel’sprinciplesFormulatingandtestinggenetichypothesis(遺傳學(xué)假說的形成和檢驗)Mendelianprinciplesinhumangenetics(人類遺傳學(xué)中的孟德爾原理)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(雙子葉)andatrue-breeding(純種).Onepeculiarityofpeareproductionisthatthepetalsofflowerclosedowntightly,preventingpollengrainsfromenteringorleaving.2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance73MonohybridCrosses:thePrinciplesofDominanceandSegregation2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance8柱頭雌蕊花藥雄蕊去勢的2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance92022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance10Mendelinferredthatthesehybridscarriedalatentgeneticfactorfordwarfness,onethatwasmaskedbytheexpressionofanotherfactorfortallness.Clearly,thehybridsthathehadmadebycrossingtallanddwarfvarietieshadtheabilitytoproducedwarfprogenyeventhroughtheythemselvesweretall.2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance11Hesaidthelatentfactorwasrecessive(隱性)andthattheexpressedfactorwasdominant(顯性).Theserecessiveanddominantfactorsseparatedfromeachotherwhenthehybridplantsreproduced.Thisenabletoexplainthereappearanceofthedwarfcharacteristicinthenextgeneration.2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance12Thesefactorsarenowcalledgenes;theirdominantandrecessivearecalledalleles.Allelesarealternateformsofagene.Genescomeinpairs.Eachofparentalstrainscarriedtwoidenticalcopiesofagene—inmodernterminology,theyarediploidandhomozygous(純合子).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.這是一個創(chuàng)舉2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance17Thegenotypeisthegeneticconstitutionofacell,anorganism,oranindividual(i.e.thespecificallelemakeupoftheindividual)usuallywithreferencetoaspecificcharacterunderconsideration

基因型是一個細胞、一個生物或一個個體的遺傳構(gòu)成形式(比如組成個體的特定等位基因)，通常與其控制的特殊性狀相關(guān)。2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance18Aphenotypeisanyobservablecharacteristicortraitofanorganism:suchasitsmorphology,development,biochemicalorphysiologicalproperties,orbehavior.表型是一個生物可以被觀察到的特征或性狀：如形態(tài)、發(fā)育、生化或生理學(xué)的性質(zhì)或行為。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個假設(shè)為基礎(chǔ)):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(金魚草)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(卡方檢驗)2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance46ComparisonoftheobservedandexpectedresultsandcalculationofX2

foranintercrosswithhybridsnapdragons.2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance47Thedegreeoffreedom(自由度)Criticalvalue(可信區(qū)間)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顯性：軟骨發(fā)育不全、短指、先天性夜盲、皮膚彈性過度綜合征、Huntington氏病、馬凡氏綜合癥、神經(jīng)纖維瘤、苯硫脲嘗味試驗、克夫相、羊毛狀發(fā)隱性：白化病、尿黑酸癥、共濟失調(diào)毛細血管擴張、囊性纖維瘤、杜氏肌無力、半乳糖血癥、糖原存儲癥、苯丙酸尿癥、鏈狀細胞貧血、Tay-Sachs病等2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance51Thisiswidowspeak!這是一個長壽的顯性表型？中國人的美人尖！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(囊性纖維瘤).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(遺傳咨詢)2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance60Pedigreeshowingtheinheritanceofhereditarynonpolypoidcolorectalcancer.2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance61Inthisexamplethechildrenfallintotwopossiblephenotypicclasses.Becausethereareonlytwoclasses,theprobabilitiesassociatedwiththevariousoutcomesarecalledbinomialprobabilities(二項可能性).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玉米粒的顏色和轉(zhuǎn)基因無關(guān)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(遺傳學(xué)假說的形成和檢驗)Mendelianprinciplesinhumangenetics(人類遺傳學(xué)中的孟德爾原理)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(雙子葉)andatrue-breeding(純種).Onepeculiarityofpeareproductionisthatthepetalsofflowerclosedowntightly,preventingpollengrainsfromenteringorleaving.2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance723MonohybridCrosses:thePrinciplesofDominanceandSegregation2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance73柱頭雌蕊花藥雄蕊去勢的2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance742022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance75Mendelinferredthatthesehybridscarriedalatentgeneticfactorfordwarfness,onethatwasmaskedbytheexpressionofanotherfactorfortallness.Clearly,thehybridsthathehadmadebycrossingtallanddwarfvarietieshadtheabilitytoproducedwarfprogenyeventhroughtheythemselvesweretall.2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance76Hesaidthelatentfactorwasrecessive(隱性)andthattheexpressedfactorwasdominant(顯性).Theserecessiveanddominantfactorsseparatedfromeachotherwhenthehybridplantsreproduced.Thisenabletoexplainthereappearanceofthedwarfcharacteristicinthenextgeneration.2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance77Thesefactorsarenowcalledgenes;theirdominantandrecessivearecalledalleles.Allelesarealternateformsofagene.Genescomeinpairs.Eachofparentalstrainscarriedtwoidenticalcopiesofagene—inmodernterminology,theyarediploidandhomozygous(純合子).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.這是一個創(chuàng)舉2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance82Thegenotypeisthegeneticconstitutionofacell,anorganism,oranindividual(i.e.thespecificallelemakeupoftheindividual)usuallywithreferencetoaspecificcharacterunderconsideration

基因型是一個細胞、一個生物或一個個體的遺傳構(gòu)成形式(比如組成個體的特定等位基因)，通常與其控制的特殊性狀相關(guān)。2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance83Aphenotypeisanyobservablecharacteristicortraitofanorganism:suchasitsmorphology,development,biochemicalorphysiologicalproperties,orbehavior.表型是一個生物可以被觀察到的特征或性狀：如形態(tài)、發(fā)育、生化或生理學(xué)的性質(zhì)或行為。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個假設(shè)為基礎(chǔ)):eachgenesegregatesitsalleles,andthesesegregationsareindependentofeachother.Thesecondassumptionimpliesthatthereisnoconnectionorlinkagebetweenthesegregationeventsofthetwogenes.Forexample,agametethatreceivesWthroughthesegregationofthetexturegeneisjustaslikelytoreceiveGasitistoreceivegthroughthesegregationofthecolorgene.2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance94Dotheexperimentaldatafitwiththepredictionsofouranalysis?2022/12/19Thebasicprinciples2022/12/21Thebasicprinciplesofinheritance95Mendelconductedsimilarexperimentswithothercombinationsoftraitsandineachcaseobservedthatthegenessegregatedindependently.Theseresultsofthesesexperimentsledhimtoathirdkeyprinciple:ThePrincipleofIndependentAssortment:

Theallelesofdifferentgenessegregate,oraswesometimessay,assort,independentlyof