Meiosis
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  • 1. Meiosis
    • Similar in many ways to mitosis
    • Several differences however
      • Involves 2 cell divisions
      • Results in 4 cells with 1/2 the normal genetic information.
    • Vocabulary:
      • Diploid (2N) - Normal amount of genetic material
      • Haploid (N) - 1/2 the genetic material.
    • Meiosis results in the formation of haploid cells.
      • In Humans, these are the Ova (egg) and sperm .
      • Ova are produced in the ovaries in females
        • Process is called oogenesis
      • Sperm are produced in the testes of males.
        • Process is called spermatogenesis
    • Meiosis occurs in 2 phases: Meiosis 1 & Meiosis 2
  • 2. Spermatogenesis & Oogenesis
  • 3. Meiosis I.
    • Prior to division, amount of DNA doubles
  • 4. Metaphase 1
    • During metaphase 1 homologous chromosomes line-up along the metaphase plate
    • Areas of homologous chromosomes connect at areas called chiasmata
  • 5. Crossing Over
    • Segments of homologous chromosomes break and reform at similar locations.
    • Results in new genetic combinations of offspring.
    • This is the main advantage of sexual reproduction
  • 6. Anaphase 1
    • During anaphase 1, each homologous chromosome is pulled to opposite sides of the cell. Unlike mitosis, THE CENTROMERES DO NOT BREAK .
    • Nuclei may or may not reform following division.
    • Cytokenesis may or may not occur.
  • 7. Meiosis II
    • DNA does not double
    • Chromosomes randomly line-up along metaphase plate like regular mitosis.
    • During anaphase 2, CENTROMERES BREAK and each chromosome is pulled to opposite sides of the cell.
    • Nuclei reform and cytokenesis usually occurs (although it is often unequal).
  • 8. Overview of Meiosis