医学遗传学：种群的遗传与变异

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1、GeneticVariationinPopulationsZHANGXian-Ning,PhDE-mail:zhangxianning@zju.edu.cnTel：13105819271;88208367Office:A713,ResearchBuilding2008/09LearningObjectivesThenatureandamountofgeneticvariationinhumanpopulations,andtheroleofgeneticvariationinliabilitytodisease.EthnicGroups:C

2、aucasoid,Negroid,MongoloidGenesinHumanPopulationsStudyofdistributionandfrequencyofgenesinpopulationsreasonsfordifferentgenefrequenciesindifferentpopulations‘burdenofgeneticdisease’isrelatedtofrequencyandseverityofgeneticdisorders-toanindividualandtothepopulationasawhole.Me

3、ndelianpopulationAninterbreedingpopulationofsexuallyreproducingindividualssharingacommongenepool.Genepool,genotypes,andgenefrequencyGenepool:thegeneticconstitutionofapopulationofagivenorganism.Allthegenesofalltheindividualsinpopulationmakeupthegenepool.Genotypes:thegenetic

4、constitutionofasingleindividual.Genefrequency(allelicfrequency):thefrequenciesofthemembersofapairofallelegenesinapopulation.PhenotypefrequencyHardyWeinbergEquilibriumThelawthatrelatesallelefrequencytogenotypefrequency,usedinpopulationgeneticstodetermineallelefrequencyandhe

5、terozygotefrequencywhentheincidenceofadisorderisknown.assumes:largepopulationrandommatingnonewmutationsnoimmigrationinorout.(HardyWeinbergequationp2+2pq+q2=1)IfallallelesatalocusareeitherAora,frequencyof“A”inthepopulationisp,frequencyof“a”inthepopulationisqthenp+q=1and,fre

6、quencyofAAisp2aaisq2Aais2pqAAAaaAaap22pqq2homozygousnormalcarriersaffected(p2+2pq+q2=1)Observedfrequencyofrecessivediseaseinpopulationisq2(e.g.,frequencyofPKU=1/10000)q2=1/10000therefore:q=1/100(*thisisnotthecarrierfrequency)Sincep+q=1p=1–q=1–1/100=99/100Carrierfrequency(2

7、pq)2pq=2(99/100x1/100)=2(~1x1/100)=2/100=1/50ProbabilitythatacouplewillhaveachildwithPKU(i.e.q2)istherefore1/50x1/50x¼=1/10000GenotypeAAAa+aAaaFrequencyp22pqq2PhenotypeNormalCarriersAffectedExceptionstoHardyWeinbergAssumptionsMigration–introduction/lossofallelesMutations–m

8、ayoccuratdifferentfrequencyindifferentpopulations3.Smallpopulationsize-geneticisolate/fou