The hardy-weinberg principle acts as a null hypothesis to test whether evolution or nonrandom mating is occurring at a particular gene. Inbreeding and assortative mating change genotypic frequencies but not allele frequencies. Sexual selection leads to the evolution of traits that help individuals attract mates. Natural selection is not the only agent responsible for evolution. Mechanisms to shift allele frequencies: natural selection: increases frequency of alleles that contribute to reproductive success, genetic drift: random change in allele frequency (stochastic (without direction) uctuations, gene flow: when individuals leave one population, join another, and breed. Introduction and removal of alleles from populations leads to a change in allele frequencies. Equalizes allele frequencies between populations: mutation: new alleles are introduced, modifying allele frequencies. 25. 1 the hardy-weinberg principle: create mathematical models to predict the fate of alleles over time under various conditions, collect data to test predictions made by the models, apply results to solve problems.