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Understanding Oogenesis, Spermatogenesis, Fertilization, and Early Animal Development

This comprehensive overview explores the differences between oogenesis and spermatogenesis, as well as the hormonal influences on the menstrual cycle, examining key hormones like LH, FSH, estrogen, and progesterone. It describes the intricate process of fertilization, detailing the steps from sperm-egg binding to the acrosomal reaction, fast and slow blocks to polyspermy, and egg activation. Furthermore, the stages of cleavage, gastrulation, and organogenesis highlight early embryonic development, including the formation of critical structures from each germ layer necessary for successful mammalian development.

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Understanding Oogenesis, Spermatogenesis, Fertilization, and Early Animal Development

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  1. Ch. 46/47 Warm-Up • (Ch. 46) How do oogenesis and spermatogenesis differ? • (Ch. 46) How do these hormones affect the menstrual cycle? • LH • FSH • Estrogen • Progesterone • (Ch. 47) Describe the process of fertilization.

  2. Chapter 47Animal Development

  3. What you must know: • The events that occur when a sperm contacts an egg • What occurs in cleavage, gastrulation, and organogenesis • Two structures derived from each germ layer

  4. Mammalian Fertilization • Sperm binds to receptors in zona pellucida (extracellular matrix of egg) • Acrosomal reaction: sperm releases hydrolytic enzymes to digest z.p. (Sea Urchins) Depolarization of membrane: prevent other sperm from binding = fast block to polyspermy • Sperm + Egg Fuse • Cortical reaction: sperm + egg fusion triggers release of Ca2+ • cortical granules fuse with z.p.  z.p. hardens to form fertilization envelope = slow block to polyspermy • Ca2+ release also triggers activation of the egg

  5. Fertilization in mammals

  6. Cleavage: rapid mitotic cell division • Zygote cytoplasm partitioned into smaller cells (blastomeres) • Solid ball of cells = morula • Blastula (hollow ball of cells) filled with fluid (blastocoel) • Blastocyst (human)

  7. Gastrulation: rearrange cells to form 3-layered embryo w/primitive gut * For AP Test, you should know at least 2 derivatives of each germ layer.

  8. Organogenesis: development of 3 germ layers into organs • Notochord – stiff dorsal skeletal rod, forms from mesoderm • Neural plate  neural tube brain and spinal cord • Neurulation – forms hollow dorsal nerve chord • Somites – blocks of mesoderm arranged along notochord; sign of segmentation

  9. Early human embryonic development

  10. Amniotic embryos (reptiles, birds, mammals) Amnion Allantois Embryo • Develop in fluid-filled sac w/in a shell or uterus • Amnion: fluid protects embryo – prevent dehydration, cushions mechanical shock • Yolk : nutrients in egg • Mammalian eggs: little stored food Amniotic cavity with amniotic fluid Albumen Shell Yolk (nutrients) Yolk sac Chorion

  11. Patterns of development • Cytoplasmic determinants: chemical signals such as mRNAs and transcription factors, influence pattern of cleavage • Induction: interaction among cells that influences their fate, cause changes in gene expression • Totipotent cells: capable of developing into all the different cell types • all cells of mammalian embryos are totipotent until the 16-cell stage

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