Population bottlenecks often result in reduced or no genetic …人口瓶颈往往导致减少或没有遗传…课件.ppt

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1、Populationbottlenecksoftenresultinreducedornogeneticvariation.Smallpopulationsexperiencegeneticdrift,founderevents,andpopulationbottlenecks.Eachcausesalossingeneticvariation.Allelebecomesfixed=novariation.+geneticdrift***Summarizetheresults.Whatisthepotent

2、ialconsequenceforsmallpopulations?Populationsize%polymorphicgenesAssortativemating:whenindividualschoosematesnon-randomlywithrespecttotheirowngenotypes.Negative:matesdiffergenetically-->increasesproportionofheterozygotesMostindividualsdothistoavoidinbreedi

3、ng.Positive:likematingwithlike(includesinbreeding)-->increasesproportionofhomozygotesPositiveassortmentincreasestheproportionofhomozygotesunmasksdeleteriousrecessivealleles=inbreedingdepression***Doesitdirectlychangeallelefrequenciesoronlythefrequenciesofg

4、enotypes?%homozygositydependsonlevelofinbreeding.***Whataremechanismstoavoidinbreeding?dispersalrecognitionofcloserelativesnegativeassortativematinggeneticself-incompatibility***Whencaninbreedingbebeneficial?Individualiscapableofreproductionwithoutpollinat

5、orormateOrganismsareadaptedtolocalconditions--->besttoretaingenotypeandnotmixup.Optimaloutcrossingdistance:***Summarizethemainresults.Provideapossibleexplanationforthem.Geneflow(migration)-->mixesallelesbetweensubpopulationsandhomogenizesthem.Maintainsgene

6、ticvariation***Whatrepresentsgeneflowinanimals?plants?Animals:dispersaloftheadultanimalorgametesPlants:dispersalofpollenandseedsGeneflowimpededbyaphysicalbarrier.Doseparatedpopulationshaveadifferentgeneticstructure?Willthisleadtospeciation?Evolutionbynatu

7、ralselection…Finchesbeaksizechangesinresponsetochangeinseedhardnessindroughtyears.Naturalselection:changeinthefrequencyoftraitsinapopulationbecauseofdifferentialsurvivalandreproductionofindividualswiththosetraits.Individualswiththemostoffspringareselected

8、andtheproportionoftheirgenotypesincreasesovertime.Fitness:thegeneticcontributionbyanindividualtofuturegenerations.Relativefitness:Maximum=1=mostfitTypesofnaturalselection:IntermediatesmostfitExtremesmostfitTw