The Inherently Feminine Embryonic Plan and Testosterone Induction of the Male Secondary Sex
In Part II, we saw that the primary (gonadal) sex of mammals is indeed determined by a genuine genetic difference between the sexes. The constitutive production of testis-organizing H-Y antigen by male embryos diverted the embryonic gonad’s inherent tendency to develop into an ovary and caused the testicular organization. Although the constitutive expression of H-Y antigen is, as a rule, associated with the male-specific occurrence of the Y chromosome, in exceptional species and individuals we have seen that in a very strict sense, it is the expression or nonexpression of H-Y antigen rather than the presence or absence of the Y that determines the fate of embryonic gonads. With the successful organization of testes, the task assigned to the male-specific gene, has been accomplished regardless of whether it represents the H-Y structural gene or. its regulator. Although the Y chromosome may perform a few other tasks, such as preventing the manifestation of the webbed neck and exceptionally short stature in the absence of the second X in man or ensuring the motility of spermatozoa in the mouse, such peripheral problems do not belong to the realm covered by this book.
KeywordsExternal Genitalia Urogenital Sinus Wolffian Duct Fetal Testis Fetal Testosterone
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