Hardy-Weinberg Equilibrium

Allele frequencies, genotype ratios, and conditions for genetic equilibrium

The Hardy-Weinberg principle states that allele and genotype frequencies in a population remain constant from generation to generation in the absence of evolutionary forces. Five conditions must be met: (1) no mutation, (2) random mating, (3) no natural selection, (4) infinite population size (no genetic drift), and (5) no gene flow (migration). Given allele frequencies p and q (where p + q = 1), genotype frequencies are AA = p², Aa = 2pq, aa = q². When any condition is violated, evolution occurs. Natural selection changes frequencies based on fitness differences. Genetic drift causes random fluctuations more pronounced in small populations. Mutation introduces new alleles at low rates. Migration introduces alleles from other populations. Non-random mating (assortative mating, inbreeding) changes genotype but not allele frequencies.