Form of cell division in which gametes are formed.

Key terms:

  • Homologous chromosomes – pair or set of chromosomes
  • Tetrads – A set of identical sister chromatids
  • Chromatid – one half of a replicated chromosome
  • Chromatin – Combination of DNA and Proteins in nucleus

Steps in Meiosis

  1. Interphase: DNA replicated
  2. Prophase I
    • Chromatin condenses into chromosomes
    • nuclear membrane breaks down
    • centrioles (in animals) migrates to poles of the cell and form spindle fibers which attach to each homologous chromosome pair
  3. Metaphase I
    • tetrads line up at metaphase plate
  4. Anaphase I
    • homologous chromosomes separate and move to opposite ends of the cell
  5. Telophase I / cytokinesis
    • nuclear membrane reforms
    • cytokinesis: contractile ring at center pinches cells apart into 2 haploid daughter cells
  6. Prophase II
    • nuclear membrane breaks down
    • cromatin condenses into chromosomes
    • spindle fibers from centrioles form and attach to chromatids
  7. Metaphase II
    • chromosomes line up at cell center (metaphase plate)
  8. Anaphase II
    • Sister chromatids separate and move towards opposite ends of the cell
  9. Telophase II / cytokinesis
    • reform nuclear membranes
    • chromatids reform into chromatin
    • spindle breaks down

A difference between male and female gametes.

  • Male → 4 gametes
  • Female → 1 viable gamete, 3 polar bodies

In cytokinesis, the majority of the cytoplasm is saved for one egg. This increases its fitness to be nourished and grow.