Selection. Let a be a recessive sex-linked gene, and suppose that a selection process makes mating of a-males impossible. If the genotypes AA, Aa, aa appear among females with frequencies u, 2v, w, show that for female descendants of the first generation u = u + v, 2v = v+w, w = 0, and hence p = p +9, 91-19. That is to say, the frequency of the a-gene among females is reduced to one-half.