Social mechanisms in the population genetics of Tay‐Sachs and other lethal autosomal recessive diseases: A computer simulation model

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Abstract
A computer simulation model was developed to study the effects of various feudal social customs on the incidence of lethal autosomal recessive genes. Populations of 500 individuals were created in which each person was characterized by sibship, genotype, and sex. The numbered sibships were sorted into numerical order. Each individual then sought a mate from 6 or 12 sibships on either side of his or her own sibship. The resulting couples were sorted in order of the husband's sibship number, after which the couples produced children in accordance with the prevailing birth rate. This ordering of sibships made the probability of a gene remaining in one locality higher than the probability of it drifting to distant localities.A lethal autosomal recessive gene was introduced into populations at a starting carrier rate of 10%. This fell after 20 generations to 2.54 ± 0.17% (SEM) which was significantly less than the 5.00% carrier rate predicted by a deterministic model in which random mating occurred in an infinite population. The excessive loss of the lethal gene was caused by the high incidence of consanguineous marriages and by the occurrence of random inequalities in the distribution of the gene. The avoidance of sib marriages raised the final carrier frequency (3.28 ± 0.19%) as did reproductive compensation (4.33 ± 0.26%). The combination of the incest taboo and reproductive compensation raised the final carrier rate to 5.05 ± 0.28%. It is concluded that the social factors which may have operated over a period of many centuries in the past have had a significant effect on the population genetics of lethal autosomal recessive genes.