Hardy Weinberg

The Hardy–Weinberg principle (also known as the Hardy–Weinberg equilibrium)

- that allele and genotype frequencies in a population will remain constant from generation to generation in the absence of other evolutionary influences. These influences include non-random mating, mutation, natural selection, genetic drift, and gene flow.

  Because one or more of these influences are typically present in real populations, the Hardy–Weinberg principle describes an ideal condition against which the effects of these influences can be observed.

For example, a single fly with two alleles with frequencies (A) = p and (a) = q, respectively, the expected genotype frequencies are (AA) = p2 for the AA homozygotes, (aa) = q2 for the aa homozygotes, and (Aa) = 2pq for the heterozygotes. The genotype proportions p^2, 2pq, and q^2 are called the Hardy-Weinberg proportions. p + q must be equal to 1, and p^2 + 2pq + q^2=1.