Sex Determination and Differentiation

The biological sex of a human being is dependent on a genetic pathway starting from the chromosomal set that determines the differentiation of the gonads. In this chapter the current knowledge of the physiological genetic regulation of gonadal development, termed sex determination is described, followed by the endocrine differentiation into the usual phenotypes of male and female. The delicate complexity of these pathways is not only dependent on the genetic composition, but needs to occur in a stringent step-wise and time-dependent manner, therefore dependent on hitherto often unknown regulatory mechanisms. Deviations and disruptions of these pathways may lead to disorders or differences of sex development (DSD), demonstrating that the poles of female and male may be not robust, but are subject to high variability even within the usual sex development.