Social selection in human populations: fitness modification of offspring by an affected parent at two loci.

The effect of social reaction to a disease at one locus (the B locus) on the frequencies of deleterious genes at that locus and another locus (the A locus) has been studied. Social reaction is formulated so that affected parents at the B locus reduce or increase their offsprings' fitnesses. It has been shown that the genotype frequencies at the two loci depend strongly on the social reaction, but, because the magnitude of linkage disequilibrium is very small, the gene frequency at each locus can be treated as if each locus were segregating independently. Consequently, the model can be extended so that many rare diseases can be considered simultaneously.