Mutation adaptation and genetic variation

All living organisms exist under the constant threat of mutation. The rate at which mutations arise and their fitness effects are two of the most important quantities in evolution. The majority of mutations are believed to be deleterious, and many common features of life have probably evolved at least in part as a response to deleterious mutations. These features include diploidy, outcrossing and sexual reproduction and recombination. Despite the commonness of fitness-reducing mutations, some mutations must be beneficial, and these supply the raw material for adaptive evolution. The proposed research investigates three aspects of the evolutionary biology of mutations. In the first, we will explore the causes of sperm-biased mutation transmission in plants, a phenomenon recently discovered in our lab. Male-biased mutation had been documented in mammals and birds, where it was proposed to result largely from the greater number of cell divisions in the male than in the female germ line. This cell-division hypothesis should not apply to plants, so the discovery in plants shows that other causal processes must be operating. The second major thrust of the proposed research will study the mutation rate and the advantages of sex and recombination using the yeast Saccharomyces cerevisiae. The rate of mutation and the spectrum of fitness effects are two of the most important yet unresolved issues in evolutionary biology. The third major part of the proposed research investigates the maintenance of genetic variation in plant populations differing in rate of self-fertilization. Using both molecular and quantitative genetic measures, we will quantify the degree to which self-fertilization causes a change in genetic variation, and thus may contribute to the apparent lack of persistence of highly self-fertilizing lineages over evolutionary time.