Meiosis

• differences to mitosis

  • 2 cell divisions
  • 4 identical daughter cells
  • haploid, not diploid
  • 2 anaphase
• Phases of meiosis

  1. DNA replicates
  2. chromosomes condense
  3. 2 sister chromatids joined by a centromere, nucleus dissolves
  4. metaphase 1
  5. anaphase 1
  6. cytokinesis 1
  7. metaphase 2
  8. anaphase 2
  9. cytokinesis 2
• Metaphase 1

  • spindle fibres attach to centromere, form from centrioles and are positioned by cytoskeleton
  • chromosomes line up along the equator in pairs
  • crossing over and random assortment
• Anaphase 1

  • spindle fibres pull chromosomes to either pole
  • pulls homologous pairs to opposite poles
• Cytokinesis 1

  • nucleus forms
  • cytoplasm divides
  • 2 identical daughter cells are produced
  • haploid
• Metaphase 2

  • chromosomes line up along the equator
  • spindle fibres extend from centriole and attach to centromere
• Anaphase 2

  • sister chromatids separate
• Cytokinesis 2

  • nucleus forms
  • cytoplasm splits
  • 4 genetically unique daughter cells
  • haploid
• Number of cells at the start of division?

  1
• Is the parent cell haploid or diploid?


  Diploid
• number of cells at the end of division?

  4
• Are daughter cells haploid or diploid?


  hapolid
• Are daughter cells identical to parent cells?

  no
• are daughter cells identical to each other?

  no
• In humans, how many chromosomes are there at the beginning of division?

  46
• In humans, how many chromosomes are there at the end of division?

  23
• How many divisions occur?

  2
• in what type of cells does meiosis occur?

  gametes
• what is the purpose of meiosis?

  • producing sperm and eggs
  • allows for genetic variation
  • haploid