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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What will be an ideal response?
These cells begin the second mitotic division in spermatogenesis
A) primary spermatocytes B) spermatogonia C) spermatids D) secondary spermatocytes
The zygomaticus major muscle
A. puckers the mouth for kissing. B. contributes to pouting. C. contributes to laughing and smiling. D. causes crow's feet wrinkles. E. raises the eyelid.
Which of the following features distinguishes skeletal muscle from smooth muscle?
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