Haploid, single-gene model of natural selection... WA PWA P Wa p(1+ s) p' = = PWA + (1 -p)wa 1 + ps P WA + (1 -p) . p = frequency of A allele WA = 1+ s, where s is a "selection coefficient" Wa . 1- p = frequency of a allele . s > 0 when A is favoured; s