meiosis

• Meiosis


  The process of cell division that produces gametes (sex cells) with half the normal number of chromosomes
• Meiosis


  • Occurs in sex cells (germ cells) and produces gametes
  • A reductional division resulting in haploid cells
  • Involves two sequential divisions resulting in four cells
  • Produces cells that are genetically different because of genetic recombination (crossing-over)
• Genes


  Sections of DNA that influence one or more hereditary traits in an individual
• Alleles


  One of two or more versions of DNA sequence (a single base or a segment of bases) at a given genomic location

  
• Chromosomes in humans


  • 46 chromosomes
  • 23 paired sets of chromosomes
  • X+X=female, X+Y=male
  • Karyotype

  
• Stages of meiosis


  1. Meiosis I (reductional division)

  2. Meiosis II (equational division)
• Stages of meiosis I

  1. Interphase

  2. Prophase I

  3. Metaphase I

  4. Anaphase I

  5. Telophase I

  6. Cytokinesis I
• Interphase of meiosis I

  • G1 phase
  • S phase
  • G2 phase
• Prophase I


  • Leptotene
  • Zygotene
  • Pachytene
  • Diplotene/Diakinesis
• Meiosis I


  • Homologous chromosomes separate
  • Daughter cells have half the chromosome number of parent cell
• Stages of meiosis II

  1. Prophase II

  2. Metaphase II

  3. Anaphase II

  4. Telophase II

  5. Cytokinesis II
• The end result of meiosis II is four non-identical, haploid daughter cells
• Difference between meiosis I and meiosis II

  In meiosis I, a pair of homologous chromosomes separate to produce two diploid daughter cells. In meiosis II, sister chromatids separate to produce four haploid daughter cells. No genetic recombination by crossing over occurs in meiosis II.
• Meiosis is a beautiful dance of chromosomes that ensures the continuity of life