Random allele frequency changes in finite populations, without selection
The Wright-Fisher model samples the next generation's allele count from a binomial:
k ~ Binomial(N, p')
where p' = p(1+s) / [p(1+s) + (1-p)]
In neutral drift (s=0), fixation probability of a new mutation = 1/N. Mean fixation time = 4N generations (diploid). Mutation-drift balance: heterozygosity H ≈ 4Nμ/(1+4Nμ).
Kimura's neutral theory (1968): most molecular variation is selectively neutral — drift dominates at the molecular level.