The Y chromosome and primary sexual differentiation.

The mammalian Y chromosome plays a dominant role in initiating fetal testicular differentiation. Testicular differentiating genes on the Y chromosome can be serologically detected as H-Y antigen. The correlation of numerical and structural abnormalities of the X and Y chromosomes, combined with H-Y antigen reactivity, gonadal histology, and phenotype, has contributed to mapping the locus of these genes on the Y chromosome and has elucidated some of the mechanisms responsible for anomalous primary sexual differentiation. The causes for failure of gonadal differentiation despite the presence of a Y chromosome or for testicular differentiation in the absence of a detectable Y are discussed. Evidence is presented for genes on the X chromosome that regulate the activity of testicular differentiating genes on the Y chromosome.