Mechanisms that impact allele frequencies

gene flow

new alleles that enter the gene pool change allele frequencies

genetic drift

any change in allele frequency, small populations are more likely to be affected by random chance, can eventually lead to an allele becoming completely fixed or lost

rapid decrease in population—bottleneck

caused by natural disaster or man-made disaster, the few who survive create a new gene pool with the alleles

rapid decrease in population—founder’s effect

a few individuals from a larger population break off and colonize a new location, causes a reduction in genetic diversity

mutation

random-passing-on of alleles during mating

selection

works on phenotypes not genotypes, is a cost-benefit tradeoff—all traits have pros and cons, the strength of the selective pressure dictates the rate of change