Allele Frequency from Genotype Counts

With N individuals, p = (2·AA + Aa) ÷ 2N and q = 1 − p. Under Hardy-Weinberg equilibrium the expected genotype frequencies are p², 2pq and q². A chi-square comparison against the observed counts tests for equilibrium (1 degree of freedom; χ² above 3.84 means a significant departure at 5%).