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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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