gamete formation (homo sapiens) gamete formation (homo sapiens)
TRANSCRIPT
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GAMETE FORMATION
(Homo sapiens)
GAMETE FORMATION
(Homo sapiens)
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Anaphase I
Growth and
maturation
SPERMATOGENESIS HumanHuman65 days65 days
Spermatogonium (stem cell)
Primary Spermatocyte
• Prophase I
• Metaphase I
• 2N = 4 (humans 2N = 46)
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Anaphase II
Spermiogenesis
Secondary Spermatocytes
• Prophase II
• Metaphase II• N = 2 (humans N = 23)
Spermatids
N = 2 (humans N = 23)
Sperm
• Four functional cells
• N = 2
(humans N = 23)
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Growth and maturation
OOGENESIS
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
Anaphase I
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)
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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
Anaphase II
Male pronucleus
Ovum & 2nd Polar Body
• One functional cell
• N = 2 (humans N=23)
• Male & female pronuclei fuse to form zygote
• Polar bodies degenerate
1stPolarbody
2nd Polar bodies
Oocyte
Ovum