In
population genetics, the Hardy–Weinberg principle is a relationship between the frequencies of
alleles and the
genotype of a population. The occurrence of a genotype, perhaps one associated with a disease, stays constant unless matings are non-random or inappropriate, or mutations accumulate. Therefore, the frequency of genotypes and the frequency of alleles are said to be at "genetic equilibrium". Genetic equilibrium is a basic principle of
population genetics.
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In an infinitely large population, gene and genotype frequencies remain stable as long as there is no selection, mutation, or migration. For a bi-allelic locus where the gene frequencies are p and q: p2+2pq+q2 = 1. Link to a lecture on
H-W.