Sex Determination from an Evolutionary Perspective: The Mammalian Regulatory Model.

Sex determination varies greatly among animal species including mammals. Although two identical (XX) or distinct (XY) gonosomes are found in all species of the latter, the ratio of sex-specific content varies considerably ranging from a small minority in monotremes to more than 90% in primates. However, the similarities are strong enough to allow us to study those mechanisms in comparison with each other and obtain useful information on the evolution of sex determination. The paper focuses on the basic principles of sex determination in mammals, stressing the common evolutionary background behind the striking similarities observed even among phenotypically and geographically distinct species. Sequencing and comparative genetic data seem to suggest that a common evolutionary origin for all mammalian sex determination strategies is most probable. Nevertheless, original research data is still required for the understanding of the complex underlying mechanisms. [ABSTRACT FROM AUTHOR]