The Endocrine Role in Mammalian Sexual Differentiation

Abstract

The hormones play an essential role, in all species, in the development and function of ovaries and testes, but in most species with Y-determined sexual differentiation, administration of androgens or estrogens does not cause sex reversal. This chapter explains the mechanism by which genetic sex is ultimately translated into phenotypic sex because the mechanisms are different in the two types of mammals. In the marsupial, chromosomal directly dictates major aspects of the sexual phenotype. There is some evidence that genetic factors may control directly at least one sexually dimorphic trait in the eutherian mammal: one or more Y-linked traits appear to influence height and tooth size independent of endocrine function. The human Y chromosome has been mapped by YAC cloning, but the specific gene(s) responsible for these growth phenomena has not been identified. The mechanisms by which the sexual phenotypes form in man and marsupial may not be totally dissimilar. In both, major components are controlled by testicular hormones and there is a direct genetic component, the difference being that the direct genetic sex contribution to the male phenotype is less important in the eutherian mammal.