Meiosis

• There are two kinds of cell divisions, mitosis and meiosis
• When cells divide by mitosis, two identical daughter cells are

  formed, with the same number of chromosomes as the mother cell

  and each other
• Mitosis forms all cells in our bodies except the gametes
• In meiosis, four cells (gametes) with half the number of

  chromosomes are formed. They are genetically different to each other
• During meiosis, the parent cell must do two things:

  • It must copy each chromosome (replication)
  • It must divide twice so that each daughter cell receives

  just one chromosome from each homologous pair
• During the first division, one chromosome from each homologous

  pair goes into each daughter cell
• During the second division, the chromosome separates into two

  parts, one in each daughter cell
• Four genetically different gametes produced
• Body cells have two sets of chromosomes and gametes have one set of chromosomes
• All gametes are genetically different from each other
• Gametes join at fertilisation to restore the full number of chromosomes (46 in humans) to form a zygote
• The zygote divides by mitosis to increase the number of cells to form an embryo
• As the embryo develops, the cells differentiate (they become specialised)