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

在大多数哺乳动物中，未分化胚胎的性别取决于Y染色体的存在与否：雄性是XY，雌性是XX。然而，如果Y染色体不能触发男性，就会产生XY雌性。XY雌性在人类和家鼠中都存在，但频率极低，因为人类XY雌性是不育的，而家鼠是不育的。然而，在8种野外小鼠中(Akodon属)，XY雌性鼠的出现频率很高(10%-40%的雌性鼠是XY鼠)，并且完全能生育。初步的物种谱系表明，这些Akodon XY雌性至少独立起源了六次。一旦XY雌性起源，她们也必须生存。计算机模型和DNA序列多态分析将有助于阐明哪些进化机制起到维持XY雌性的作用。阿科登生殖生物学的两个不同寻常的特征似乎很重要。首先，XY母亲生的XY女儿比XX女儿多。其次，XY雌性往往比XX雌性更容易生育--XY母亲一生中产生更多的后代。这种不同寻常的性染色体系统为了解新的性别决定系统是如何进化的提供了一个独特的机会。此外，了解维持XY雌性的进化力量有助于阐明新的基因类型是如何维持的，从而说明遗传多样性是如何存在的。最后，比较Akodon和人类的性染色体可能有助于理解为什么Akodon XY雌性可以生育，而人类却不育。

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.