Glossary

Genetic equilibrium is a term referring to the stability in the frequency of an allele across generations. We may assume genetic equilibrium in large populations that are not being greatly influenced by genetic drift or new mutations and in which selection of mates is mostly random.

A rigorous notion of genetic equilibrium was first proposed independently by G.H. Hardy and Wilhelm Weinberg at the start of the 20th Century; the Hardy-Weinberg principle states that a population should be in equilibrium with respect to a specific gene as long as five conditions hold:

1. The population is so large that random changes in the allele frequency are negligible.
2. No new mutations are affecting the gene;
3. The gene does not influence survival or reproduction, so that natural selection is not occurring;
4. Gene flow, or the change in allele frequency due to migration into and out of the population, is negligible.
5. Mating occurs randomly with respect to the gene of interest.