Meiosis

• Meiosis stages

  
• Prophase 1

  1. Chromosomes are visible

  2. Nuclear envelope disintegrates

  3. Bivalent form (non-sister chromatids attach at points called centromeres)

  4. Crossing over occurs

  5. Cell membrane intact

  6. Centrioles move to the poles

  7. Microtubule spindles are synthesised
• Metaphase 1

  1. Bivalents line up along Equator

  2. Chromosomes line up in a random order
• Anaphase 1

  1. Spindle attaches to centromeres

  2. Spindles pull apart chromosomes in each bivalent to opposite poles

  3. Centromeres don't divide

  4. Chiasmata separate
• Telophase 1

  1. 2 nuclear envelopes form around each set of chromosomes

  2. Cytokinesis occurs
• Interphase in animal cells

  • Very short
  • Chromosomes uncoil
• Interphase in plant cells

  • Straight into meiosis II
• Prophase 2

  1. Chromosomes are visible

  2. Nucleolus disappears

  3. Nuclear envelope disintegrates

  4. Cell membrane intact

  5. Centrioles at the poles 90° to previous position in meiosis I

  6. Microtubules are synthesised
• Metaphase 2

  1. Chromosomes line up along equator

  2. Spindle attaches to centromeres

  3. Chromatids are randomly arranged
• Anaphase 2

  1. Cell membrane divides, separating the chromatids

  2. Spindles pull apart chromatids of each chromosome to opposite poles
• Telophase 2

  1. Nuclear envelopes form around genetic information in genetically unique daughter cells

  2. In animal cells: Cytokinesis

  3. In plant cells: Cell plate forms where the equator was