The Hardy-Weinberg principle The Hardy-Weinberg principle: the frequency of alleles and genotypes in a population?s gene pool will remain constant from one generation to the next. Provided that only Mendelian segregation and recombination of alleles are at work Describes a population that is not evolving The Hardy-Weinberg principle describes a hypothetical population Changes to allelic frequency and genotype always occur in real populations The equation p2 + 2pq + q2 = 1 p2 and q2 represent the frequencies of the homozygous genotypes 2pq represents the frequency of the heterozygous genotype Conditions of the Hardy-Weinberg Principle Population size = extremely large No gene flow can occur (no immigration or emigration of individuals) No mutations No natural selection