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Abstract

Plant genomes are sculpted by the combined influences of mutation, selection, and genetic drift. As a result of these processes, genome size, as well as the overall architecture of genomes, is constantly fluctuating. A species’ genomic architecture can impact what types of genetic variants give rise to phenotypic variation, including variation in hybridization efficiency which can lead to the formation of genetic barriers. The genomic, phenotypic, and reproductive consequences of genome evolution in Arabidopsis thaliana and its relatives were examined and three major findings are discussed. 1. Transposable elements (TEs) are a major source of variation in genome architecture and their fast, often lineage-specific, evolution can swiftly alter a species’ epigenetic landscape as a result of their tightly linked epigenetic marks, including DNA methylation. As a result of this rapid evolution, any TE-induced phenotypic consequences are not maintained for long periods of time. 2. The contribution of genetic drift and selection to generating or maintaining the genetic variants underlying hybrid phenotypes was evaluated in a large collection of first generation hybrids. Mutation-selection balance is not sufficient to explain the detected loci, and either genetic bottlenecks or adaptive processes are also contributing to the variants underlying hybrid phenotypes. 3. The species-wide frequency of intraspecific genetic barriers that arise as a byproduct of genome evolution was characterized in Arabidopsis thaliana. A molecular signature of hybrid dysfunction, segregation distortion, was surveyed in a large set of genetically diverse F¬2 populations and distorted loci were uncovered in 12-24% of populations, indicating that a number of genetic barriers are segregating in this species.