L3 Devnt I - Embryogenesis/development Fertilization...

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Embryogenesis/development Fertilization Cleavage Gastrulation Neurulation Organogenesis Cytodifferentiation Free-living larva, metamorphosis  to adult = INDIRECT  DEVELOPMENT Mini-adult = DIRECT  DEVELOPMENT
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Germ cells - spermatozoa • Production begins at puberty • 300 – 500 million sperm per ejaculate • assuming 50 x 50 x 500 million  = 1,250,000,000,000 cells for 1.8 fertilisations!
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Homunculus Hartsoeker  1694 Preformationists Spermatozoa
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Germ cells - oocytes • Productions begins as a 1 month embryo • by 5 months produced 7 million • most die, by birth approx 1 million left • stuck in 1 st  meiotic prophase until ovulation • 400,000 by puberty • only use 13 x 30 = 400 • oocytes can be 40+ years old
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Meiosis female male 2n 4n 2n 1n DNA synthesis DNA synthesis 4 sperm 1 egg 1 st  meiotic division 2 nd  meiotic division
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Primary oocytes Human = 0.15mm coelacanth = 90mm (200 million x volume) Zona pellucida (chorion, micropyle) Corona radiata follicle
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Eggs Yolk platelets – vitellogenesis
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L3 Devnt I - Embryogenesis/development Fertilization...

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