GAMETE FORMATION (Homo sapiens)

SPERMATOGENESIS Growth and maturation Anaphase I Human 65 days Spermatogonium (stem cell) Growth and maturation Primary Spermatocyte Prophase I Metaphase I 2N = 4 (humans 2N = 46) Anaphase I

Anaphase II Spermiogenesis Secondary Spermatocytes Spermatids Sperm Prophase II Metaphase II N = 2 (humans N = 23) Anaphase II Spermatids N = 2 (humans N = 23) Spermiogenesis Sperm Four functional cells N = 2 (humans N = 23)

OOGENESIS Growth and maturation Anaphase I Oogonium (stem cell) Divide mitotically beginning at 2 months gestation until about 7 million cells (6-7 months gestation) All but 1-2 million die Growth and maturation Primary Oocyte Remains in a modified Diplotene stage 2N = 4 (humans 2N = 46) Resume meiosis at about 12 years of age & continue until about 45 years (mature eggs may be 12 to 45 years of age) Anaphase I

Anaphase II Secondary Oocyte & 1st Polar Body About 400, one day longevity Cytoplasm conserved for ovum N = 2 (humans N=23) Secondary oocyte dies at metaphase II if no sperm penetration Oocyte 1st Polar body Anaphase II Ovum & 2nd Polar Body One functional cell N = 2 (humans N=23) Male & female pronuclei fuse to form zygote Polar bodies degenerate Ovum 2nd Polar bodies Male pronucleus