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Mitosis v Meiosis Workshop

We are going to look at the chromosomes ask Dr Chromo! , their number and shape and see what happens to them in the two types of cell division.

Consider an individual with four pairs of chromosomes. The four pairs are drawn below, in the circle. In each pair, one chromosome is darker than the other one. This shows that one comes originally from the father of this individual and the other one from the mother. In our example,

  • how many chromosomes has the cell?
  • how many pairs?

    • In somatic ask Dr Chromo! cells : mitosis

    A somatic cell is any cell of an organism which is not a germ cell

    Mitosis is a simple, single cell division .

    In germ cells : meiosis

    Germ cells are cells that divide into gametes

    Meiosis is a more complex process , with two cell divisions.

    During metaphase, chromosomes can be seen to have two chromatids ask Dr Chromo! . The separation occurs between chromatids of the same chromosome.

    Locate

  • a chromosome,
  • a pair of chromosomes,
  • a chromatid.
    		• During the first stages of meiosis, the chromosomes of the same pair are very close to each other.

    During metaphase of the cell division, the chromosomes are all situated at the equator, but they are not touching each other...

    They can't exchange any material.

    Then, the chromatids separate.

    		The chromatids of a chromosome exchange material with a chromatid of its matching pair. That is what is illustrated above. This event is called "crossing over".

    Note how different the chromatids are now.

    Locate

  • a chromosome,
  • a chromatid,
  • a pair of chromosomes.
    • The chromosomes separate at this stage. What is different from mitosis at this stage?
    Both cells divide again. This time the chromatids separate.
    This is the end of mitosis

    How similar are the two daughter cells :

    • to each other?
    • to their mother cell?

    What happened to the mother cell?

    Try to think about the advantages and disadvantages of mitosis.

    About Meiosis
  • How many cells do we have at the end?
  • How many chromosomes in each cell?
  • Do we have pairs?
  • What will happen to these cells?
  • What are the advantages of meiosis?

    • Try to think of the mechanism of reproduction and the events occuring then.



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