Overview Forces responsible for genetic variation mutation de novo mutation rates constant among populations login to view 1 more bullet founder effect if one member of a small community carries a triat, as the population expands there will be a higher frequency of that trait in the new community than there is in the general population Ex.) Pennsylvania Amish and Ellis-van Creveld syndrome genetic drift a dramatic change in allele frequency based on chance login to view 1 more bullet natural selection ↑ in allelic frequency that ↑ species fitness ↓ in allelic frequency that ↓ species fitness some genes ↑ species fitness as heterozygote but ↓ species fitness as a homozygote login to view 1 more bullet bottleneck Even when fitness is equal for all phenotypes, a population bottleneck can result in disrupted allelic frequencies or loss of a genotype all together by chance gene flow transfer of alleles from one population to another Hardy-Weinberg equilibrium states that genotype and allele frequencies remain constant through generations disease prevalence equation p2+ 2pq + q2 = 1 login to view 5 more bullets requirements for validity large population random mating the genotypic frequencies of the population will remain stable from generation to generation assumptions no mutation no selection for any of the genotypes at the locus no migration other notes prevalence of an X-linked recessive disease in males = q login to view 1 more bullet possible to assume in most cases that p = 1 as the wild-type allele is approximately 1