Dissertation Research: Evolution and Maintenance of XY Females in Natural Populations of South American Rodents (Rodentia: Genus Akodon)

点击翻译按钮获取中文摘要

Edwards9902337In most mammals, the sex of an undifferentiated embryo hinges on the presence or absence of the Y chromosome: males are XY and females are XX. If however the Y chromosome fails to trigger maleness, XY females can result. XY females exist in both humans and house mice, but at extremely low frequencies because human XY females are infertile and house mice are subfertile. However, in eight species of field mice (genus Akodon) XY females exist at high frequencies (10-40% of females are XY) and are fully fertile. Preliminary genealogies of species suggest that these Akodon XY females have originated at least six times independently. Once XY females originate, they also have to survive. Computer models and analysis of DNA sequence polymorphisms will help illuminate which evolutionary mechanisms act to maintain XY females. Two unusual features of Akodon reproductive biology appear to be important. First, XY mothers produce more XY daughters than XX daughters. Secondly, XY females tend to be more fertile than their XX counterparts--XY mothers produce more offspring over their lifetime.This unusual system of sex chromosomes offers a unique opportunity to understand how new sex-determining systems evolve. Additionally, understanding the evolutionary forces that act to maintain XY females illuminates how novel genotypes are maintained, and thus how genetic diversity exists. Finally, comparisons between Akodon and human sex chromosomes may aid in understanding why Akodon XY females are fertile but humans are infertile.