CIE A Level Biology (9700) 2019-2021

Revision Notes

16.1.3 Role of Meiosis in Gamete Formation in Animals & Plants

Role of Meiosis in Gamete Formation in Animals & Plants

  • Meiosis is a type of cell division that halves the number of chromosomes
  • Meiosis is involved in the process of gamete formation (gametogenesis) in many animals and plants

Gametogenesis in humans

  • In humans gametes are produced in organs called the gonads
  • The male gamete is the sperm cell and it is produced in the testes by spermatogenesis
  • The female gamete is the egg cell and it is produced in the ovaries by oogenesis
  • There are three common phases that occur during the process of gametogenesis in both males and females:
  1. Multiplication / proliferation: the cells in the germinal epithelium layer divide by mitosis to produce multiple cells that have the capacity to become gametes
  2. Each of these cells goes through a growth phase
  3. Maturation: haploid gametes are formed from these cells via meiosis
  • The maturation phase differs substantially between sperm and egg cells
  • For sperm cells:
    • Meiosis I produces two secondary haploid spermatocytes that are the same size
    • Both of these then undergo meiosis II to form four gametes
  • For egg cells:
    • Meiosis I produces one haploid secondary oocyte and a smaller, haploid, polar body which disintegrates
    • Meiosis II is similar as it produces a single, large, haploid egg cell and another smaller polar body that is also lost
    • Only one gamete is formed at the end of oogenesis
  • There are some differences in timing between spermatogenesis and oogenesis
  • In males:
    • All the stages of spermatogenesis take place in the testes after puberty
    • A single male can produce millions of sperm cells each day throughout his life
  • In females:
    • Thousands of primary oocytes are formed in the embryonic ovaries, prior to birth
    • Most of these primary oocytes remain in prophase II until fertilization by a sperm cell stimulates the completion of meiosis II

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Lára graduated from Oxford University in Biological Sciences and has now been a science tutor working in the UK for several years. Lára has a particular interest in the area of infectious disease and epidemiology, and enjoys creating original educational materials that develop confidence and facilitate learning.

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