Ecology 182 review.docx

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Ecology 182 review542013Nonrandom mating and inbreeding depressionrandom matingRequirements in order to hold the Hardy Weinberg equilibriumNo selectionLarge populationNo migrationNew mutationNonrandom mating with respect to genotypeSelectionsmall populationmigrationno new mutationInbreedingWhen mating individuals are more closely relatedthan those drawn at randomOutbreedingWhen mating individualsare less closely related than those drawn at random Neither inbreeding or outbreedingcauses a change in allelic freqenciesInbreeding and outbreeding differ from selection genetic drift migration and mutation all of which alter allelic frequenciesInbreeding and outbreeding causes a change in genotypic frequencies Inbreeding frequency of the homozygous increases frequency of the heterozygous decreases Most extreme form of inbreeding is selffertilization plantsfrequency of heterozygotes decreases by 50 in each generationEquation for changes in genotype frequencies22p2pqq1generation 02pqgeneration 0pqgeneration 1pq2generation 2OutbreedingFrequency of the homozygous decreasesFrequency of the heterozygous increasesBecause allelic frequencies do no change with inbreeding it only takes one generation of random mating to reestablish the original genotypic frequencies in the population even after 1000 or more generations of selffertilizationsThis happens with selffertilization inbreeding and outbreedinggenerally Inbreeding depression the coupling of inbreeding and selectionWith both selection and inbreeding we can alter allelic frequenciesInbreeding depressionNatural populations contain significant number of deleterious recessive allelesuse inbreeding depression to alter allelic frequenciesRecessive alleles have deleterious effects are masked in heterozygotes where the presence of one copy of the normal allele is sufficient to produce the needed amount of functional polypeptides Inbreeding results in an increase in the frequencies of homozygotes in the popThis means that there will be a larger proportion of the offspring with two copies of the deleterious alleles The frequency of the deleterious alleles AA where A is the 222 recessive allelewhen a larger proportion of the offspring carry two copies of the recessive allele mortality rates increase
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