Sex Determination and Gonadal Development

In mammals, sex determination is a result of chromosomal constitution determined at fertilization, with females harboring XX and males XY sex chromosomes. The apparent simplicity of this system belies the intricate genetic and cellular interactions that direct differentiation of the bipotential gonadal primordium into either a testis or an ovary. These organs house, nurture, and direct the differentiation of the germ cells, which in turn are required for reproduction and for transmission of genetic information to future generations. Specification, migration, and differentiation of germ cells are controlled by the somatic cell environment. Once sex differentiation has occurred, the germ cells are directed to develop into oocytes (female) or spermatozoa (male), both highly specialized cell types. This chapter traces the key events in the genesis of the mammalian germline, and describes how genetic and cellular control mechanisms in the gonadal somatic cell lineages influence the development of germ cells.