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Early Development
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Early Development

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  1. Early Development • Gametes

  2. Sperm

  3. Egg • Lecithal = Yolk

  4. Microlecithal egg Small amount of yolk Amphioxus Eutherians

  5. Mesolecithal egg • Medium amount of yolk • Amphibians

  6. Macrolecithal egg • Large amount of yolk • Bird and reptiles • Most fish

  7. Isolecithal • Even yolk distribution • In microlecithal eggs

  8. Telolecithal • Uneven yolk distribution • Macrolecithal and Mesolecithal eggs • Vegetal Pole – yolk region • Animal Pole – relatively yolk-free, high metabolic activity/embryo

  9. Amniote eggs Amnion Allantoic cavity Amnionic cavity Allantois Albumin Chorion Yolk

  10. Layers around egg • Vitelline membrane • Jelly • Capsule • Shell • Albumin • Corona Radiata • Zona Pellucida

  11. Oviparous

  12. Viviparous

  13. Ovoviviparous

  14. Fertilization

  15. Internal Fertilization • Apodans • Urodeles • Amniotes

  16. External Fertilization • Fish • Frogs

  17. Zygote

  18. Cleavage & BlastulaMicrolecithal Eggs Cleavage – Mitosis divisions Blastomeres Blastocoel

  19. Cleavage & Blastula • Blastocyst in mammals • Inner cell mass in mammals • Trophoblast cells in mammals

  20. Cleavage & BlastulaMesolecithal eggs

  21. Cleavage & BlastulaMacrolecithal Eggs • Blastoderm • Blastocoel

  22. Gastrulation • Germ layers form from which ALL future organs form • Notochord forms • Bilateral symmetry established

  23. Gastrulation/Microlecithal eggs • Involution • Blastopore • Archenteron

  24. Germ layers • Ectoderm –outer layer • Mesoderm – middle layer • Forms notochord • Splits to form coelom • Endoderm – inner layer around archenteron

  25. GastrulationMesolecithal eggs • Epiboly

  26. Ectoderm • Nervous System • Sensory structures • Neural crest cells that become melanocytes, adrenal gland… • Epidermis of skin • Epithelium of mouth/nose and anus

  27. Endoderm • Lungs & Swim bladders • Digestive viscera

  28. Mesoderm • Chordomesoderm becomes notochord

  29. Mesoderm • Dorsal Mesoderm = Epimere • Segmented bands called somites • Divides into • Dermatome • Myotome • Sclerotome

  30. Mesoderm • Lateral plate mesoderm = hypomere • Splits into Somatic and Splanchnic layers • Coelom between these layers

  31. Hypomere • Somatic Mesoderm plus Ectoderm = • Somatopleure • Splanchnic Mesoderm plus Endoderm = • Splanchnopleure