Sexual differentiation of the embryo is normally determined by:
A. the number of chromosomes, with males having 22 pairs and females having an extra pair of XX chromosomes.
B. the presence of two X chromosomes, which causes the primordial testes to degrade.
C. the presence of one Y chromosome, which causes the primordial ovaries to degrade.
D. the presence of the Y chromosome, which directs the undifferentiated gonads to develop into testes (when there is one X chromosome present as well).
E. hormones produced by the placenta.
D
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