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Abstract
The following chapters are the result of my work investigating the roles of two potential genetic preadaptations to domestication: recombination and diversity. Two chapters directly address this possibility, testing hypotheses about the preadaptive value of recombination or diversity. The remaining two chapters extend these results, investigating further aspects of the roles of diversity and recombination in domestication. In chapter 1, I use data on chiasma frequencies available from almost a century of plant cytogenetical literature to test two hypotheses regarding the role of recombination in plant domestication. I show that recombination does not function as a preadaptation, but is instead selected indirectly by the process of domestication itself. In my second chapter I investigate genetic diversity and effective population size as potential preadaptations to domestication. I develop a forward population genetic simulation model to test the preadaptive role of effective population size, and compare these results to patterns of genetic diversity in the genus Zea. The results suggest that effective population size may well function as a preadaptation to domestication for many crop plants. In chapter 3 I address the effect of genome size on recombination. I analyze the relationship between genome size and recombination rate in a phylogenetic context, and though I find a significant positive correlation, I am also able to show that domestication still explains meaningful differences in recombination even after genome size is taken into account. In my final chapter I look at the effects of domestication on patterns of allozyme diversity and quantitative genetic variation for fruit and leaf size in tomatillo, Physalis philadelphica, I find that domestication has had little effect on overall levels of tomatillo diversity but that wild and weedy accessions nonetheless harbor diversity not found in cultivated types. I also show that directional selection on fruit size during tomatillo domestication has had a dramatic effect on patterns of quantitative genetic diversity in cultivated populations, and that this pattern of variation is unexpectedly found for leaf size but not leaf shape characters as well.