Accumulation of Nonfunctional Genes on Sheltered Chromosomes

The probability of accumulation of nonfunctional mutations on sheltered chromosomes such as the Y-chromosome in higher organisms is studied by using diffusion approximations in probability theory. It has been shown that this probability is highly dependent upon the effective population size, the heterozygous effect of nonfunctional mutations, and the recombination value between the sex-determining and nonfunctional gene loci. The present knowledge of these three factors, which has been obtained mostly from Drosophila studies, suggests that the nonfunctional genes could be accumulated on sheltered chromosomes within a reasonable period of evolutionary time.