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UBC Theses and Dissertations

Theoretical models of the genetics of adaptation Griswold, Cortland K.

Abstract

This thesis presents models that predict the effects of genetic factors contributing to an adaptation when mutations act pleiotropically and when populations are spatially substructured. When mutations act pleiotropically, it is possible for a mutation to have both beneficial and deleterious effects on different phenotypic characters. In chapter two, I quantify the fraction of mutations that are fixed by selection that have deleterious pleiotropic effects on a given character. Results show that as the degree of pleiotropy increases the frequency of deleterious fixed effects on a character increases. In chapter three, I present the expected relationship between the effects of a fixed mutation on phenotypic characters. Results show that the expected correlation among the effects of a fixed mutation is usually less, sometimes much less, than the mutational correlation. Furthermore, I show that as the beneficial effect of a fixed mutation on one character becomes large, the expected size of a pleiotropic effect on another character approaches the expected size of a random mutation given the effect on the first character. Chapter four addresses a model in which characters that are affected by mutations that have limited or no pleiotropic effects are postulated to evolve more quickly than ones that are affected by mutations that have pleiotropic effects. I present new results showing conditions under which an increase in pleiotropy has no effect on the rate of adaptation or actually increases the rate of adaptation. In chapter five, I give the expected distribution of effects of mutations that contribute to local adaptations in a species that is substructured, experiencing heterogeneous selection, and when there is migration between local populations. I show that when two populations exchange migrants, mutations with larger phenotypic effects tend to cause more of the overall phenotypic difference than when populations are isolated. In a QTL study this means that the average percent variance explained by a QTL allele will be greater, on average, when there is migration than when there is not.

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