Inbreeding and Homozygosis

Abstract

The elementary evolutionary process in a Mendelian population is change of gene frequency. The pressures of immigration, selection and mutation on gene frequency are supplemented by the random drift brought about by the accidents of sampling among the germ cells of each generation in any population of finite size. This last process is important as furnish-ing a basis for the nonadaptive differentiation of local races. The rate at which the process takes place is measured by the rate of decrease of heterozygosis for paired allelomorphs, not subject to other evolutionary pressure. This rate has been calculated for systems of close inbreeding by working out the consequences of every possible type of mating and giving each type its due weight in each generation. The cases investigated in this way include self-fertilization,' parent-offspring mating,2 for both autosomal and sex-linked genes, and brother-sister mating,2 also for both autosomal and sex-linked genes. This method is not practicable for larger inbreeding groups. Another method, that of path coefficients has been applied to a variety of systems of mating in the case of autosomal genes.3'4' It is the purpose of the extend these results to the case of sex-linked