Mammalian germ cells arise in the yolk sac endoderm at the caudal aspe
ct of the embryo and migrate to the mesodermally-derived gonadal ridge
early in development. After the oogonia reach the gonadal ridge, the
process of meiosis begins which coincides with the first major wave of
apoptosis of female germ cells (Coucouvanis et al., 1993). Subsequent
ly, oocytes progress to the dictyate stage of prophase I where they re
main arrested until ovulation. (C) 1998 Elsevier Science Ireland Ltd.
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