HUMAN SEXUALITY: H-Y ANTIGEN. ADAM-EVE PRINCIPLE
H-Y antigen
The Y chromosome programs the differentiation of the undifferentiated cells of the primitive gonads into testes, beginning at around the sixth week of gestation. Differentiation of the undifferentiated gonads into ovaries does not begin until the twelfth week and requires the presence of two X chromosomes and no Y.
The Y chromosome programs the undifferentiated gonads toward testicular development via a plasma membrane protein, the Y-linked histocompatibility (H-Y) antigen. Exactly how the undifferentiated gonads in XX individuals are programed into ovaries is not clear. Ohno suggests the possibility of an ovarian-organizing antigen similar to that of the H-Y antigen. This ovarian-organizing antigen has not yet been identified.
Having programed the differentiation of the gonads, the sex chromosomes have no other known direct influence on subsequent sexual behavior and psychosexual (gender identity/ role) differentiation. The program of gender identity/role differentiation and development is now carried forward by the presence or absence of secretions of the newly differentiated fetal testes. Without the secretions of the testes, morphologic differentiation is female.
Adam-eve principle
Prenatally, the program of gender identity/ role is carried forward specifically by the determinants of masculine morphologic differentiation, namely, mullerian inhibiting substance and androgen, secreted by the testes. Present knowledge of embryology indicates that fetal ovarian hormones are not essential to female morphologic differentiation. Whether or not maternal and placental hormones are essential is not known. Nature is predisposed first to make a female and only with the addition of testicular secretions does it make a male. The embryological fact that nature’s preference is female is epitomized as the Eve principle. The fact that something must be added to make a male is epitomized as the Adam principle.
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