Allele frequency dynamics — selection, drift, heterozygote advantage
Directional selection: the A allele has fitness advantage s over a. With dominance h, Aa heterozygotes have fitness 1+hs relative to aa=1. The allele frequency evolves by Δp = p(1−p)[ph + (1−2p)hs]·s / mean fitness. Drift adds binomial sampling noise proportional to 1/√N.