Population Genetical Studies on Molecular Evolution and Polymorphism of DNA Sites Linked to Selected Sites

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In this research project, I studied the following two problems.(1)A stochastic model for molecular evolution by compensatory interaction. In this study, I considered two loci where mutation occurs irreversibly from the wild type allele to a mutant allele in both loci. Genetic combinations with single mutant are deleterious. The double mutant, however, compensates the harmful effect of single mutants. For this model, the average time until fixation of the double mutant was investigated to see a possibility that the compensatory interaction is a common mechanism for molecular evolution. I showed that the linkage between the loci is an important factor and the compensatory interaction can be a mechanism for molecular evolution when the loci are linked strongly or moderately. One remarkable finding was that deleterious mutation can accelerate the speed of fixation of the double mutant. In other words, the average time until fixation of the double mutant is shorter under the existence of appropriate deleterious intermediate states.(2)The effect of autocorrelated stochastic selection on neutral polymorphism. In this study, I considered a neutral locus with 2 alleles linked to a selected locus with 2 alleles. An autocorrelated stochastic selection is operating on the selected locus. I investigated how genetic variability of the neutral locus is effected by the existence of the selected locus. I found that this effect is an inceasing function of the intensity of selection and the population size and there is an optimal mean persistent time for environmental change of the autocorrelated stochastic selection.