Development and Function of the Ovaries and Testes in the Fetus and Neonate

Abstract

Developmental sex biology may be approached at different levels: chromosomal, genetic, gonadal, and genital. Embryonic and fetal development consists of three sequential periods: (i) sexually undifferentiated, characterized by the organogenesis of the anlagen of the gonads and genitalia; (ii) sex differentiation of the gonads; and (iii) sex differentiation of the internal and external genitalia. Although the chromosomal sex of the embryo is established at fertilization, no evident difference exists between XX and XY embryos in the gonads or the genital tracts until the 6th week. From the 7th week, opposing cascades of gene expression drive the differentiation of the bipotential gonads into testes or ovaries. Internal and external genitalia virilize in the presence of testicular androgens and AMH, while they feminize in the absence of testicular hormone action.