Chapter 8 part 6 gametogenesis

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5 Terms

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Gametogenisis

Sperm and egg cells are formed by meiosis but they follow different developmental pathways!

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spermatogenisis

  • Cytoplasm distribution is roughly equal

  • But…

  • Excess cytoplasm and unnecessary organelles (everything but nucleus and a few mitochondria) is phagocytized (devoured) by specialized cells that support sperm formation – Sertoli cells.

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Oogenesis

  • Involves unequal cytokinesis


  • Start with a primary oocyte

  • After meiosis I, there is a small polar body. The secondary  oocyte has most of the cytoplasm.

    Oogenesis and the development of an ovarian follicle. Long description is available in notes, press F6

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oogenesis pt 2

  • The secondary oocyte also divides unevenly


  • After meiosis II, the mature egg has most of the cytoplasm.

  • There are three polar bodies (the first polar body also goes through meiosis II resulting in two polar bodies)

Oogenesis and the development of an ovarian follicle. Long description is available in notes, press F6

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Fertilization & Mitochondrial Inheritance

  • In humans, the entire sperm enters the egg.

  • This includes the few mitochondria present in the midpiece.


  • There is a narrative that mitochondrial DNA inheritance is maternal


  • But some paternal mitochondria can survive (one study showed 1 paternal mitochondria for every 10,000 maternal mitochondria)

  • In some species, there are actually mechanisms that eliminate paternal mitochondria

  • Many species show strict maternal inheritance. Humans just may not be among them.