| Genetic variation within a population reflects a balance of evolutionary forces, with variation introduced by mutation or gene flow, eliminated by genetic drift or by positive/purifying selection and, potentially, maintained by balancing selection. In addition, the fates of variants are tied to those of nearby sites via linkage, to an extent determined by the recombination rate. Patterns of diversity throughout the genome thus hold a very rich, albeit convoluted and partial, record of evolutionary processes. It has become common to gather variation information across multiple individuals, increasingly genome-wide, providing the data with which to describe and test the influence of these various forces globally and at particular loci. In my dissertation, I use large-scale genetic variation data to address several evolutionary questions: First, I ask what are the important determinants of overall intraspecific genetic diversity levels by compiling and analyzing genetic diversity estimates from the literature for eukaryotic species. I find some intriguing patterns, but mainly highlight how much is still unresolved. Next, I use the genetic variation within two species, chimpanzees and humans, to look for evidence of loci under long-term balancing selection, a mode of selection for which conclusive signatures have been difficult to find and whose prevalence in nature is long debated. I find at least six loci with strong evidence that balancing selection has acted since before the species split, suggesting that long-term balancing selection may be more common than currently believed. Finally, using recombination events inferred from human pedigrees, I estimate the heritability of recombination phenotypes and conduct a genome-wide association study to identify genetic variation contributing to differences in recombination rates and patterns between individuals. These studies demonstrate how population patterns of genetic variation can provide insight into the action of selection and the genetic basis of recombination. |
