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		Lecture 30: Gametogenesis, Hormones & Reproduction Campbell, 5th, 913- mid 918, mid 922-92 (Campbell, 4th, 937-942, mid 947- mid 953) I. Gametogenesis A. Germ cells 1. Distinct cell lineage - remain totipotent/ uncommitted Gametogenesisis the production of gametes. The cells that can do this, the reproductive cells or germ cells, are set aside early in embryogenesis. While the other cells of the embryo are becoming specialized, able to make liver cells, skin cells, brain cells, etc., the germ cells remain uncommitted. 2. Differentiation dependant on gonad In fact, they're even uncomitted as to whether to give rise to sperm or eggs. The primordial germ cells colonize the gonad even before it has differentiated into an ovary or a testis. a. Testis i. Mitotic arrest If it becomes a testis, the Sertoli cells organize the germ cells into cords. After a few rounds of cell division, the germ cells enter mitotic arrest(they stop dividing) until after birth. They begin to divide again at puberty. ii. SpermatogenesisFigure 46.12 iii. Sperm Figure 46.11 Male germ cells form a self-renewing stem cell population called spermatogonia They behave rather like meristem cells in plants. They undergo asymetric cell divisions where one daughter remains a stem cell while the other begins to differentiate. In this case, differentiate means entry into meiosis, which produces 4 haploid cells which all develop into sperm. During this whole process, they are supported and nourished by the Sertoli cells of the testis. As the haploid cells differentiate, the nucleus become highly compacted and they develop specialized organelles. Eventually, they leave most of their cytoplasm behind and become sperm. As in the sea urchin, the mammalian sperm is a highly specialized cell type It has a flagellato move with, lots of mitichondriato supply energy, a compacted nucleusto deliver DNA and the acrosome, a large vesicle filled with	. .