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Meiosis Tutorial

A review of meiosis

Comparing Meiosis and Mitosis

  • Chromosome behavior
    1. Mitosis: Homologous chromosomes independent
    2. Meiosis: Homologous chromosomes pair forming bivalents until anaphase I
  • Chromosome number- reduction in meiosis
    1. Mitosis- identical daughter cells
    2. Meiosis- daughter cells haploid
  • Genetic identity of progeny:
    1. Mitosis: identical daughter cells
    2. Meiosis: daughter cells have new assortment of parental chromosomes
    3. Meiosis: chromatids not identical, crossing over

Meiotic errors

  • Nondisjunction- homologues don't separate in meiosis 1
    1. Results in aneuploidy
    2. Usually embryo lethal
    3. Trisomy 21, exception leading to Downs syndrome
    4. Sex chromosomes
      1. Turner syndrome: monosomy X
      2. Klinefelter syndrome: XXY
  • Translocation and deletion: transfer of a piece of one chromosome to another or loss of fragment of a chromosome.

Mitosis, Meiosis, and Ploidy

  • Mitosis can proceed independent of ploidy of cell, homologous chromosomes behave independently
  • Meiosis can only proceed if the nucleus contains an even number of chromosomes (diploid, tetraploid).
  • Trisomy 21 does not prevent meiosis

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