Date

2019

Document Type

Dissertation

Degree

Doctor of Philosophy

Department

Integrative Biology

First Adviser

Lang, Gregory I.

Abstract

From sticklebacks to insects to mice, closely related populations encountering similar selective pressures tend to evolve parallel phenotypes. The era of genomics has revealed that some instances of parallel phenotypes are caused by similar mutations in similar genes. Others cases of parallel adaptation are shown to be driven by mutations in distinct genes. These observations spark an open question in evolutionary biology; given identical starting points and selective pressures, how repeatable should we expect molecular adaptation to be? Laboratory evolution of model organisms presents an ideally suitable system for beginning to answer this question. This work uses experimental evolution of Saccharomyces cerevisiae combined with genomics and functional genetics to ask questions about the repeatability of evolution. We focus on identifying and examining the adaptive consequence of molecular events that arise more often than expected by chance. We find extensive parallelism in ploidy evolution when genome duplication proves adaptive. We use whole genome sequencing to identify loci targeted by selection multiple independent times across populations. We use one of these loci, STE4, to examine how dominance constrains mutation and adaptation. We then leverage the extensive gene-level parallelism we observe to detect genetic interactions and measure the effect of epistasis on genotype evolution.

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