THE MOLECULAR-GENETICS OF HUMAN SEX DETERMINATION

The classical conception of the chromosomal mechanism of sex determination presumes a chromosome unique for and determining the heterogametic sex. On the basis of recent evidence, however, this picture is becoming increasingly complex, with a multitude of genes appearing to interact simultaneously or successively to bring about the gonadal phenotype. The genes identified so far that are thought to be involved in the process of human sex determination are distributed on various chromosomes, but the consecution of their function remains to be elucidated. To the Y chromosome only a relative role can be ascribed, and it has not yet been established which gene is on top of the cascade. All of the genes under discussion are involved in transcriptional control, and at least the majority of them appear to exert pleiotropic effects. The regulation of their expression must still be defined, and it will be a long way before a link to gonadal morphogenesis is ultimately found.