Evolution of a Finite Population Under Gene Conversion

Evolution at a multiallelic locus under the joint action of gene conversion, mutation, selection, and random genetic drift is studied. Generations are discrete and nonoverlapping; the diploid, monoecious population mates at random. Under the assumption that all four evolutionary forces are weak, a diffusion approximation is established for the dynamics of the gene frequencies. For two alleles, the inclusion of gene conversion merely alters one of the two selection parameters of the thoroughly investigated diffusion process without conversion. Therefore, all results for this classical process, some of which are reviewed and extended here, are immediately applicable to the biologically more general problem. Small conversional disparities can dramatically affect the fixation probability (and hence the rate of gene substitution) and can greatly reduce the mean conditional fixation time of a new mutant. The mean absorption and fixation times are often sufficiently short to imply that biased gene conversion can be an important mechanism for the loss of genetic variability in and the genetic divergence of isolated populations.