Co-evolution of genomic structure and selective forces underlying sexual development and reproduction.

Genomic structure affects the expression and evolution of phenotypes via its effect on genomic function. One example is the presence of sex chromosomes and the development of the sexual phenotype. Multiple forces account for the evolution of genomic structure and function, some acting synergistically and some in an antagonistic manner, in a co-evolutionary process between genomic architecture and environmental effects at different time scales. Here I review the evolution of sex chromosomes and how they affect sex determination, sex ratios, sexual selection, and sexual conflict, at the same time that these phenomena influence the evolution of genome organization. Because of this reciprocal interaction, the need to correctly identify sex chromosome systems in order to understand the causes and consequences of their evolution is emphasized. Importantly, it is argued that the existence of taxa lacking sex chromosomes poses a challenge to current evolutionary models and a unique opportunity to test them empirically using reptiles as a model system.