Meiosis

• The steps of prophase 1 ...

  1. DNA condenses
  2. Nuclear membrane disappears
  3. Centrioles move towards opposite poles in animal cells
  4. Spindle develops
  5. Homologous chromosomes come together
  6. Bivalents form
  7. Chiasmata form
  8. Genetic exchange occurs
• The steps of metaphase 1 ...

  1. Random assortment of homologous chromosomes in bivalents at the equator of the cell
  2. Each chromosome is attached to the spindle by its centromere
• The steps of anaphase 1 ...

  1. Spindle fibres contract
  2. Chromosomes in each bivalent separate
  3. Chromosomes are pulled towards opposite poles of the cell
• The steps of telophase 1 ...

  1. This is the end of the first meiotic division
  2. Chromosomes have reached opposite poles
  3. Nuclear membrane reforms around each group of haploid chromosomes
  4. This results in 2 haploid cells
• The steps of prophase 2 are ...

  1. DNA condenses
  2. Nuclear membrane disappears
  3. Nucleolus disappears
  4. Centrioles move towards opposite poles
  5. Spindle develops at right angles to the old spindle
• The steps of metaphase 2 are ...

  1. Chromosomes line up separately on the spindle fibres at the equator
  2. Each chromosome is attached to the spindle by the centromere
• The steps of anaphase 2 are ...

  1. Spindle fibres contract
  2. Centromeres split
  3. Chromatids pulled towards opposite poles of the cell
• The steps of telophase 2 are ...

  1. On reaching the poles the chromatids lengthen
  2. Spindle disappears
  3. Nuclear membrane reforms
  4. Cytokinesis occurs
  5. 4 haploid cells are the result
• How does meiosis bring about genetic variation?

  1. The homologous pairs of chromosomes cross over at chiasmata and exchange genetic material
  2. The random assortment of maternal and paternal chromosomes during metaphase 1
  3. Chromosome number is halved
  4. Each new daughter cell shows genetic variation