Evolution of Genome Size

Abstract The size of the genome represents one of the most strikingly variable yet poorly understood traits in eukaryotic organisms. Genomic comparisons suggest that most properties of genomes tend to increase with genome size, but the fraction of the genome that comprises transposable elements (TEs) and other repetitive elements tends to increase disproportionately. Neutral, nearly neutral and adaptive models for the evolution of genome size have been proposed, but strong evidence for the general importance of any of these models remains lacking, and improved understanding of factors driving the activity of TEs should also be considered. Fine‐scale investigation of the mutational and population‐genetic properties of both small and large insertions and deletions should help advance our understanding of how and why genome size evolution has occurred. Key Concepts Larger genomes tend to have larger amounts of most genome components, but the proportional representation of different types of DNA changes dramatically. Transposable elements and other repetitive DNA represent a major determinant of genome size variation. The importance of ancient whole genome duplication events in genome size evolution, particularly in plants, remains to be fully resolved. Direct estimates of mutational patterns do not suggest that the relative rate and size of small insertion/deletion events are major contributors to genome size evolution. Although broad‐scale patterns suggest a negative correlation between effective population size and genome size, comparative phylogenetic methods and comparisons of focal taxa have not suggested repeated shifts in genome size are tied to repeated changes in effective population size. The extent and causes of between‐species changes in transposable element activity should be characterised, to better understand the drivers of genome expansion.