Meiosis

• Gametes are produced by meiosis

  • gametes only have 1 copy of each chromosomes so that when gamete fusion takes place, you get the right amount of chromosomes again
  • to make gametes which only have half the original number of chromosomes cells divide by meiosis. This process involves 2 cell divisions. In humans, it only happens in the reproductive organs
• Meiosis produce cells with Half the normal number of chromosomes

  1. before the cell starts to divide, it duplicates its genetic information, forming 2 armed chromosomes - one arm of each chromosomes is an exact copy of the other arm. after replication the chromosomes arrange themselves into pairs
• Meiosis produce cells with Half the normal number of chromosomes

  2. In the first division in meiosis the chromosomes pairs line up in the centre of the cell
• Meiosis produce cells with Half the normal number of chromosomes

  3. the pairs are then pulled apart so each new cell only has one copy of each chromosome. some of the father's chromosomes and some of the mother's chromosomes go into each new cell
• Meiosis produce cells with Half the normal number of chromosomes

  4. in second division, the chromosomes line up again in the centre of the cell. the arms of the chromosomes are pulled apart
• Meiosis produce cells with Half the normal number of chromosomes

  5. you get 4 gametes, each with only a single set of chromosomes in it. each of the gametes is genetically different from the others because the chromosomes all get shuffled up during meiosis and each gamete only gets half of them, at random
• The cell produced by gamete fusion replicates itself

  • after 2 gametes have fused during fertilisation, the resulting new cell divides by mitosis to make a copy of itself
  • mitosis repeats many times to produce lots of new cells in an embryo
  • as the embryo develops, these cells then start to differentiate into the different types of specialised cell that make up a whole organism