《群体的遗传平衡》PPT课件.ppt

Chapter11PopulationGenetics第十一章群体的遗传平衡11.1Concept11.1.1Genefrequency11.1.2Genotypefrequency11.2Hardy-Weinberglaw哈迪温伯格平衡11.2.1Equilibriumingenefrequencies基因频率的恒定11.2.2Equilibriumingenotypefrequencies基因型频率的恒定,11.3Calculatingmulti-allelefrequencies复等位基因频率的计算11.4Genotypefrequenciesintheself-crossingpopulation自交群体中基因型频率的变化11.5Transferofrecessivelethalgeneintherandommatingpopulation互交群体中隐性致死基因的传递,Genesinpopulations:hardy-weinbergequilibrium群体中的基因:哈迪温伯格平衡Populationgenetics群体遗传学Deme同类群Frequency频率Genepool基因库Randomly随机地Randommating随机交配Selection选择Migration迁移,11.1ConceptPopulationgeneticsisthestudyofallelesofgenesinpopulations,andtheforcewhichmaintainorchangethefrequenciesofparticularallelesandgenotypesinpopulations.Thetotalgeneticstockofthepopulationisitsgenepool.Individualshaveaselectionofallelesfromthatgenepool,possiblytakenrandomly.,群体：随机交配(异交)，产生可育后代的动态个体群dynamic,孟德尔氏群体：基因遗传表现符合孟德尔遗传规律的群体。,群体遗传组成变化物种进化。研究群体遗传学阐明物种进化机制,群体基因库-群体中遗传物质总和,群体遗传学研究群体中维持或改变特定等位基因及基因型频率的作用力的学科。,研究基因在群体中的传递情况和基因频率、基因型频率变化的科学。,研究群体遗传结构及其变化规律的遗传学分支学科。,14.1.1Gene/allelefrequencies基因频率某群体中某一等位基因数与位点上出现的基因总数之比（该位点上可能出现的所有基因类型的频率之和等于1，p+q=1）,14.1.2Genotypefrequencies基因型频率同一基因座上某种基因型个体数与总群体数之比（群体中某基因座上所有基因型频率之和等于1，P+H+Q=1）,Eg.100个体AA30，Aa60，aa10基因型频率为：AAAaaa30%60%10%,设:PHQ(P+H+Q=100%）基因数：A60600=120a06020=80总基因数=60+60+60+20=200基因频率：p(A)=120/200100%=60%q(a)=80/200100%=40%(p+q=100%),即：p(A)=(2P+H)/(2P+H+H+2Q)=(2P+H)/2(P+H+Q)=P+1/2Hq(a)=(H+2Q)/(2P+H+H+2Q)=(2Q+H)/2(P+H+Q)=Q+1/2H即：p+q=P+1/2H+Q+1/2H=P+H+Q=1,11.2Hardy-Weinberglaw(哈迪温伯格平衡定律)HardyandWeinbergindependentlydevelopedthiscalculationtoshowthatanequilibriumingenotypefrequencieswilloccurafteronegenerationofrandommating,andthosegenotypecanbecalculatedfromallelefrequencies.Theequilibriumfrequencieswillbemaintainedfromgenerationtogenerationunlesssomeforcechangestheallelefrequencies,1908年，英国数学家Hardy、德国内科医生Weinberg分别得出该定律,Hardy和Weinberg各自独立提出此平衡式:经过一个世代的随机交配，群体中基因型频率恒定，其频率可由等位基因频率推算。这种衡定代代保持，除非某种因素改变等位基因的频率。,在一个无限大的随机交配的群体中，基因频率和基因型频率在没有迁移、突变、自然选择的条件下，世代相传不发生变化。,大群体Largepopulation无限大无遗传漂变,无迁移Noimmigration不发生迁入迁出,随机交配Randommating有性交配（泛交）机会均等且随机,基因频率和基因型频率恒定的五大条件：,无突变Nomutation无频发和非频发突变,无选择Noselection无自然选择作用,PopulationsthatsatisfyallfiveassumptionsabovearesaidtobeatHardy-Weinbergequilibrium.,11.2.1Equilibriumingenefrequencies基因频率的恒定Allelefrequenciesisfoundbyaddingupthenumberofcopiesofeachalleleinapopulationandexpressingitasafrequency.Apopulationofdiploidindividualshas2Nalleles.EachAaheterozygotehasoneAalleleandoneaallele,eachAAhomozygotehastwoAalleles,eachaahastwoaalleles.,基因频率的恒定：假设亲本交配产生精、卵配子，各配子中基因频率p(A)和q(a)；配子随机组合形成合子，其基因型：,基因型之比：p2AA:2pqAa:q2aa=p2:2pq:q2=1:2:1,子一代配子基因频率：A=(2p2+2pq)/(2p2+2pq+2pq+2q2)=p2+pq=p(p+q)=p或=P+1/2H=p2+1/22pq=p(p+q)=pa=(2q2+2pq)/(2p2+2pq+2pq+2q2)=q2+pq=q(p+q)=q或Q+1/2H=q2+1/22pq=q(p+q)=q,F1基因A频率=p；基因a频率=q；且世代相传-基因频率的恒定,e.g.亲本配子中p=0.7,q=0.3，求子代形成配子的基因频率？,letsseetheanswer,合子基因型：,子代形成配子的基因频率：A=(2p2+2pq)/(2p2+2pq+2pq+2q2)=p2+pq=0.49+0.21=0.70a=(2q2+2pq)/(2p2+2pq+2pq+2q2)=q2+pq=0.09+0.21=0.30,A、a频率仍分别为0.7和0.3群体该基因座上基因频率总和=0.7+0.3=1基因型频率总和=0.49+20.21+0.09=1,p2(AA)+2pq(Aa)+q2(aa)=p(A)+q(a)2=P+H+Q=1,11.2.2Equilibriumingenotypefrequencies基因型频率的恒定Equilibriumingenotypefrequencieswillbereachedinzygotesafteroneroundofrandommating.ThetotalexpectedgenotypefrequenciesarepredictedbytheHardy-Weinbergequation:p2(AA)+2pq(Aa)+q2(aa)Iftherearetwoalleles,Aanda,withfrequenciespandqrespectively,thentheexpectedfrequencyofAAhomozygotesisp2,ofAaheterozygotesis2pq,andofaahomozygotesisq2.,三种基因型个体间随机交配，产生的不同基因型频率为：,父本基因型及频率,母本基因型及频率,AAAaaa,全部后代的基因型频率为：P2+2PH+2PQ+H2+2HQ+Q2=P2+PH+1/4H2+PH+2PQ+1/2H2+HQ+1/4H2+HQ+Q2=(P+1/2H)2+2(1/2PH+PQ+1/4H2+1/2HQ)+(Q+1/2H)2=(P+1/2H)2+2P(1/2H+Q)+1/2H(1/2H+Q)+(Q+1/2H)2=(P+1/2H)2+2(Q+1/2H)(P+1/2H)+(Q+1/2H)2AAAaaa=p2+2pq+q2=1,后代基因型频率与亲本一致相同基因位点上的基因型频率总和为1,e.g.苯丙酮尿症隐性遗传病患者在美国的发病率为1/10000，问美国人群中，该隐性基因频率和携带该隐性基因的杂合子基因型频率是多少？,Thefrequencyofhomozygousrecessivenessisq2,sothefrequencyoftherecessivealleleisq,andthefrequencyofthedominantallelep=(1-q),解：设该隐性基因为a，杂合子基因型为Aa，发病率即纯合隐性aa基因型频率为：1/10000aa=q2=1/10000q=1/10000=0.01p+q=1p=1-0.01=0.99Aa=2pqAa=20.990.01=0.0198答:q=1%Aa=1.98%,e.g.根据实际调查数据判断是否遗传平衡群体上海中心血站1977年对500个上海居民进行M、N血型调查，发现M血型为111人，MN血型的为241人，N型的为148人，问上海人群中M、N基因频率各是多少？该群体是否处于遗传平衡状态？,血型基因型人数M基因数N基因数MMM1112220MNMN241241241NNN1480296,基因频率：p=0.463q=0.537预期平衡群体的基因型频率和人数为：P(MM)=p2=0.4632=0.2144500=108人H(MN)=2pq=20.4630.537=0.4973500=249人Q(NN)=q2=0.5372=0.2884500=145人与实际人数不符，x2测验是否在允许误差范围之内,MMMNNN实际人数111241148预期数108249145差数383x2=(d2/e)=0.33自由度取1查表得0.5p0.7为差异不显著，说明上海居民MN血型基因座位上的基因型频率处于平衡状态，为平衡群体,所以处于遗传平衡状态下的群体，一对等位基因的基因频率与基因型频率的关系为：,p=q=0.5时，AA(P)=aa(Q)=0.25Aa(H)=0.5P:H:Q=1:2:1pq,PQ;pqPQ,Judgementofequilibriumpopulation:AAAaaa10.500.250.2520.250.250.5030.640.320.044560340100,11.3复等位基因的频率计算：,e.g.假设ABO血型在某一群体中各血型基因型频率:A0.45B0.13O0.36AB0.06计算复等位基因IA、IB、i的基因频率？,A-IAIA，IAiB-IBIB,IBiO-iiAB-IAIB,设:p为IA基因频率，q为IB基因频率，r为i基因频率A:IAIA=p2,IAi=2prp2+2pr=0.45(a)B:IBIB=q2,IBi=2qrq2+2qr=0.13(b)O:ii=r2r2=0.36(c)AB:IAIB=2pq2pq=0.06解方程得：p=0.3q=0.1r=0.6,11.4自交群体中基因型频率的变化：,杂合体的连续自交纯合基因型频率上升杂合基因型频率下降,Aa自交P0-0世代杂合基因型频率，P0=1n=1P0Aa自交n=2P0AanP0/2n-自交n代后杂合基因型频率1-P0/2n-纯合基因型频率,自交-增加遗传稳定性杂交-增加遗传变异性,11.5互交群体中隐性致死基因的传递,TheunifyingconceptofpopulationgeneticsistheHardy-WeinbergLaw.Thelawpredictshowgenefrequencieswillbetransmittedfromgenerationtogenerationgivenaspecificsetofassumptions.Specifically,Ifaninfinitelylarge,randommatingpopulationisfreefromoutsideevolutionaryforces(i.e.mutation,migrationandnaturalselection),Asacheckofyourarithmeticp2(AA)+2pq(Aa)+q2(aa)whenthefrequencyqofanalleleislow,thefrequencyofoccurrenceofhomozygotes,q2,isverylow.Uncommonallelesareusuallypresentinheterozygotes,socannotbeidentifiediftheyarerecessiveandarenotexpressed,soselectioncannotactagainstthem.,e.g.玉米白化病隐性致死基因型aa设A、a频率分别p、q，起始值皆1/2，即杂合态Aa,P1F1P21/2A1/2a1/2A1/4AA1/4Aa1/2a1/4Aa1/4aaF1基因0.25AA:0.5Aa型之比=AA:2Aap=2/3q=1/3,F22/3A1/3a2/3A4/9AA2/9Aa1/3a2/9Aa1/9aaF2基因1AA:1Aa型之比p=3/4q=1/4,在隐性纯合致死效应下，显性基因频率以n+1/n+2的规律逐代递增，隐性基因频率以1/n+2的规律递减n-互交代数,crossing,群体中隐性致死基因的频率越低,显性基因的频率越高,选择系数（S-selectivecoefficient）-某一基因型在群体中被自然选择淘汰的程度S=1每传一代，该基因型全部被淘汰(如玉米白化隐性纯合个体),适合度(-fitness）-生物体将基因传给下一代的能力=1,S=0;=0,S=1,qn=q0/(1+nq0),e.g.隐性基因频率起始值为，隐性纯合致死，经过几代后，群体中该基因频率降为1/8？,Inbreedingdepression(近交衰退)Inbreedingismatingbetweenrelativesandshowingeffectsofthisonthepopulation.ItincreasesthefrequencyofhomozygotesabovethatexpectedforarandombreedingpopulationinHardy-Weinbergequilibrium.Inbreedingincreasetherateatwhichrecessivedeleteriousallelesbecomehomozygousandareremovedbyselection,sotheyhavealowerfrequencyininbredpopulations.,近交-亲缘种间的交配，使群体中纯合子频率高于平衡群体预期的频率。,近交-增加隐形有害基因纯和的频率，也增加其被选择淘汰的速率，所以隐性有害基因在近交群体中的频率较低。,MedicalimportanceThemajorityoftheraresthumangeneticdiseaseoccurasaresultofconsanguineousmarriages.Studiessuggestthatmarriagesbetweencousinshaveatleasttwotimes,anduptotentimestheratesofmiscarriageandneonatalmortalityasmarriagesbetweenunrelatedparents.,