|MadSci Network: Cell Biology|
Well, as you may already know, the purpose of both mitosis and meiosis is to take one cell and make two cells. Before the cells do this though, they have to make sure that a few things are in order. Obviously, there has to be enough stuff for the 2 cells to each be able to live independently. so, there has to be duplication of a lot of stuff before the first cell (let's call it the parent) divides. One of these things is the genome. These are the chromosomes which are made up of DNA. Once the DNA replicates (makes 2 copies of everything from what the parent originally had), the cell can divide. There are now 4 chromosomes of each type, we started out with our usual 2 of each (most organisms have 2 of each chromosome and they differ slightly from each other-this becomes important for meiosis), then when everything duplicated, we got 4!
In MITOSIS, the 2 cells that come out of the division (lets call them the daughters), are EXACTLY the same in genetic makeup as the original mother cell. They have the very same DNA and therefore make the same proteins and therefore the cells behave the same.
In MEIOSIS on the other hand, the cells are not the same at all. And in fact, this is the point of meiosis - to make new types of cells. You may know that eggs and sperm are products of meiosis, but you not only get a mixing of genes from your mother (from the egg) and father (from the sperm), but the genes inside the egg and sperm are pre-mixed because of meiosis. Thus, genetic diversity!, and an explanation for why you have traits given to you from your grandmother through your father, even though your father may not have that trait (he carries it in his genes for later mixing). This may be a complicated issue in itself but since we have 2 of every chromosome and therefore 2 of every gene (even before the DNA replication that preceeds mitosis), there's a chance that the 2 copies of the same gene are different, one of which shows up in your father and one which you have that you got from your grandmother throuh your father. The mixing, by the way comes about because after the DNA replicates in preparation for cell division. This is neat and involves chromosomes breaking apart and joining back together. Take a look at the animated movie of meiosis at http://www.biology.yale.edu/animatedMeiosis.nclk - make a point to notice the red and green chromosomes at the beginning and the mixed ones at the end.
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