The distribution of Cys282Tyr genotypes among the 30 672 white subjects in the Kaiser-Permanente epidemiologic study.

The gene frequency for the Cys282Tyr mutation was 0.0622 (q) in this population, and the frequency of the Cys282Cys (wt [wild type]), 0.9378 (p). (The His63Asp mutation does not need to be taken into account in this calculation). The Hardy-Weinberg equilibrium predicts that in a randomly breeding population, the distribution of the 3 possible genotypes (wt/wt, Cys282Tyr/wt, Cys282Tyr/Cys282Tyr) will be p2, 2 × pq, and q2. The solid bars (▪) represent these predicted frequencies; the open bars (■), the actual frequencies found in the population. It is clear that there is no deficiency of homozygotes. If this analysis were carried out on the polymorphisms that cause sickle disease, cystic fibrosis, or Tay-Sachs disease there would be a marked deficit of homozygotes in the population, since most would not have survived into middle age.