Evolution of multigene families under interchromosomal gene conversion.

A model for the evolution of the probabilities of genetic identity within and between loci of a multigene family in a finite population is formulated and investigated. Unbiased interchromosomal gene conversion, equal crossing-over between tandemly repeated genes, random genetic drift, and mutation to new alleles are incorporated. Generations are discrete and nonoverlapping; the diploid, monoecious population mates at random. Formulae for the equilibrium values of the probabilities of identity and for the rate of convergence are deduced. At equilibrium, the amount of intralocus homology, f, always exceeds the amount of interlocus homology, ĝ. The equilibrium homologies f and ĝ and the characteristic convergence time T are independent of the crossover rate. As the population size and the number of repeats increase, f and ĝ decrease and T increases; as the rate of gene conversion increases, f and T decrease whereas ĝ increases. The time T can be sufficiently short to imply that interchromosomal gene conversion may be an important mechanism for maintaining sequence homogeneity among repeated genes.