Polymorphism, divergence, and the role of recombination in Saccharomyces cerevisiae genome evolution.

A contentious issue in molecular evolution and population genetics concerns the roles of recombination as a facilitator of natural selection and as a potential source of mutational input into genomes. The budding yeast Saccharomyces cerevisiae, in particular, has injected both insights and confusion into this topic, as an early system subject to genomic analysis with subsequent conflicting reports. Here, we revisit the role of recombination in mutation and selection with recent genome-wide maps of population polymorphism and recombination for S. cerevisiae. We confirm that recombination-associated mutation does not leave a genomic signature in yeast and conclude that a previously observed, enigmatic, negative recombination-divergence correlation is largely a consequence of weak selection and other genomic covariates. We also corroborate the presence of biased gene conversion from patterns of polymorphism. Moreover, we identify significant positive relations between recombination and population polymorphism at putatively neutrally evolving sites, independent of other factors and the genomic scale of interrogation. We conclude that widespread natural selection across the yeast genome has left its imprint on segregating genetic variation, but that this signature is much weaker than in Drosophila and Caenorhabditis.