THE MOLECULAR-GENETICS OF HUMAN SEX DETERMINATION

The classical conception of the chromosomal mechanism of sex determina tion presumes a chromosome unique for and determining the heterogameti c sex. On the basis of recent evidence, however, this picture is becom ing increasingly complex, with a multitude of genes appearing to inter act simultaneously or successively to bring about the gonadal phenotyp e. The genes identified so far that are thought to be involved in the process of human sex determination are distributed on various chromoso mes, but the consecution of their function remains to be elucidated. T o the Y chromosome only a relative role can be ascribed, and it has no t yet been established which gene is on top of the cascade. All of the genes under discussion are involved in transcriptional control, and a t 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.