Genetic Drift in Populations of Distorting Gene Complexes

We use stochastic population models to study the evolution of distorting gene complexes. Distorting gene complexes, or distorters, are chromosomal regions characterized by meiotic drive: a heterozygote bearing the distorter passes it to more than 50% of offspring. Homozygotes bearing the distorting complex are sterile. Although distorters promote themselves at the expense of other genes in the same genome, they have been successful in evolution: distorting gene complexes have been observed in animal, plant and fungal species. While the molecular drive mechanisms differ, distorting gene complexes exhibit similar genetic features, suggesting that the population genetic mechanisms that allow such gene complexes to evolve may be shared. We investigate such possible mechanisms in the current work. We present Markov models and Monte Carlo simulations of genetic drift in populations of distorting gene complexes. Genetic drift, the stochastic behavior of allele frequencies in small populations, is a fundamental force in the process of evolution, yet the role of genetic drift in the evolution of distorters is not well understood. Our analysis shows how distorters evolve different characteristics in species typified by small and large populations, respectively. We apply our results to two well studied distoring gene complexes: the t-haplotype in Mus musculus and Segregation Distorter in Drosophila melanogaster.