4 Mutation pressure 5 Meiotic drive a The same mutation constantly pops up and eventually can cause evolution a Any mechanism operating differentially during meiosis in a heterozygote to produce the 2 kinds of gametes with unequal frequencies b Meaning one type is over represented 6 Natural Selection Some Agents of Genotypic Change in Detail I Inbreeding Genetic Drift and Gene Flow Chap 9 10 HWCE assumes random mating then since inbreeding is non random mating inbreeding causes evolution A Inbreeding Coefficients a f probability that an individual is autozygous i Autozygous refers to an individual who has alleles that are identical by descent must be homozygous Box 9B ii Allozygous refers to an individual who has alleles that are not identical by descent can be either hetero or homo Box 9B b F population parameter i c If F 0 for a population then i Every individual is allozygous ii The population is panmitic randomly inbreeding population iii The population is very large infinite iv The population is in HWCE with respect to this parameter d If F 1 for a population then i Every individual is autozygous ii Complete inbreeding not panmixis iii Relatively small population size finite iv Not in HWCE for this parameter e Usually natural populations are i 0 F 1 What causes inbreeding ancestor i Sib mating B Effects of Inbreeding f Consanguineous mating matings between individuals that share a recent common ii Parent offspring mating Both 1 2 can lead to autozygosity iii Self fertilization autozygosity if parent is homozygous a If F 0 then both types of homozygotes are more common than when F 0 i Inbreeding decreases the frequency of heterozygotes increases the frequency of homozygotes b If F 0 then the rate of decrease in heterozygosity is affected by the type of mating system and Ne effective population size actually reproductively successful portion i Example 1 increased relatedness of individuals in a mating leads to faster decrease in heterozygosity ii Example 2 decreased population size leads to faster decrease in c Inbreeding alone does not affect allele frequencies but it does affect genotypic heterozygosity frequencies d Inbreeding increases phenotypic variation within a species i Example when a species has demes with little or no gene flow between them inbreeding causes deme differentiation leading to phenotypically distinct demes ii Deme a local interbreeding group e Inbreeding in conjunction with natural selection can reduce the mean phenotype of a population decrease i If inbreeding increase in the frequency of the recessive homozygous genotype then the average character of the population phenotype might ii Example if A1 A1 and A2 A2 are positively correlated with viability or fecundity then inbreeding can lead to an increase in the frequency of A2 A2 which causes decreased fecundity of the population and an increased chance of population extinction iii Inbreeding Depression reduction of fitness in a population due to increased homozygosity as a result of inbreeding in populations that are normally outbreeding f Given a less than infinite population size there is going to be some level of inbreeding heterozygosity i Therefore any finite population becomes inbred over time and loses ii But the larger the population the lower the F will be and the longer time it require to reduce heterozygosity Positive Assortative Mating versus Inbreeding not the same A M preferential mating among like A M or unlike A M phenotypes Inbreeding mating between individuals more closely related than the average potential mating pair in the population Positive A M homozygosity only at those loci involved in determining the characteristics that define mating preference Versus Inbreeding over time leads to homozygosity at all loci entire genome C Genetic Drift Chap 10 a Small population size Ne promotes i Genetic Drift random changes in gene frequency b The smaller the population the more effect genetic drift can potentially have on gene frequencies Versus i Example a rock falling and killing 5 out of 1000 ii a rock falling and kill 5 out 10 c Drift causes isolated demes to become distinct from each other