Mitosis

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Mitosis is a special kind of cell division used by eukaryote cells. You will probably find a series of diagrams in your biology text book to show the stages of mitosis; these are:

  • prophase
  • metaphase
  • anaphase
  • telophase
I will add some diagrams when I have the time.
Mitosis is really a division of the nucleus into two identical nuclei. It is followed by cytokinesis which is the division of the cytoplasm into two.
Just imagine for a moment. You started your life as a single cell == a fertilized egg or zygote. THIS WAS THE FIRST YOU. By mitosis, you divided into two cells, both of your cells divided again (4) and again (8) and again(16) and again (32) and again ..... really boring but this is what you did. Now you consist of billions of cells (all genetically identical to each other). Mitosis is essential for growth and repair.
During mitosis, one cell divides into two genetically identical cells. Before mitosis starts you cannot see any chromosomes in the nucleus, however, all the DNA in the nucleus is replicated exactly. This stage is not a part of mitosis: it is called interphase (between divisions).
  • Prophase:
During prophase the chromosomes coil up. They become shorter and fatter. The nuclear envelope seems to disappear. If you squash the cell and look at it under a microscope it is possible to see chromosomes and count them. You would see 46 chromosomes in a normal human cell. This stage may take over one hour.
  • metaphase:
This is a very short stage in mitosis. The chromosomes move and line themselves up at the equator of the cell. It should be possible with a good microscope to see that each chromosome has divided into two daughter chromatids. These are genetically identical to each other. This stage only takes about 15 minutes.
  • anaphase:
During anaphase the chromatids separate (are pulled apart) and move to the poles (opposite ends of the cell). You may be able to see spindle fibres which help to pull the chromatids apart. Although this stage only takes about ten minutes, it is the most interesting stage because it shows that the cell division is genetically exact.
  • telophase:
Now there are 46 daughter chromatids at each end of the cell. Each one uncoils: it gets longer and thinner. It is no longer possible to see and count individual chromosomes.   This stage takes much longer but it is not so interesting.
After mitosis has taken place (the division of the nucleus) the cell divides into two cells. This process is called cytokinesis. New cell membrane is formed dividing the cell into two.
I am made of billions of cells, they are all genetically identical to each other and identical to my original self 54 years ago when I was a fertilized egg or zygote.
Meiosis is another kind of cell division. This is the one which makes sperms and eggs. More to follow !!!!!

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