Video narration
Why do you share traits with your relatives, while a population changes through evolution? Inherited traits come from versions of genes called alleles. Evolution happens when allele frequencies shift across generations-not when one individual transforms. Hardy-Weinberg equilibrium is the no-change baseline. For two alleles, p plus q equals one, and expected genotype frequencies are p squared, two p q, and q squared: together, one. It assumes a large population, random mating, and no mutation, migration, or natural selection; allele frequencies stay stable. Hardy-Weinberg doesn't cause evolution. It shows what no change looks like. Mutation, migration between populations, genetic drift-chance with a stronger effect in small populations-and natural selection can shift allele frequencies. Nonrandom mating can change genotype proportions without changing allele frequencies by itself. Plants and animals evolve as inherited variation shifts across generations; Hardy-Weinberg tells you what stability looks like.