The effect of social selection on population dynamics of rare deleterious genes.

Genetically abnormal or phenotypically affected individuals may influence the reproductive behaviour of other members in the family, regardless of their phenotype. This social selection is modelled by considering that whenever the normal individual has at least one affected member in the nuclear family the person has a reduced chance in mating success or in fertility compared to those from the normal nuclear family. The usual individual selection has also been incorporated using a single locus with two alleles. The gene frequency change is divided into two parts: the change due to individual selection and that due to social selection. It has been shown that a low mutation rate, a small population size and strong selection at both stages lower the equilibrium frequency of deleterious genes. The possibility of extending the single locus model for common diseases is also discussed.