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Mitosis in eukaryotes happen in this order: DNA replicates and then the cell divides. Why doesn't it happen in reverse order (i.e., cell divides and then replicates the DNA)? I am talking about diploid cells. Why has evolution favoured the first way?

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Think about what you just asked. –  mgkrebbs Sep 7 '13 at 18:22
    
I was thinking about only cells having even ploidy levels. I know it sounds stupid if we think about odd ploidy levels. –  biogirl Sep 8 '13 at 18:22
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If you are thinking of a process like meiosis but followed by DNA duplication, the problem is that this would create daughter cells that do not have the same genome as the parent cell.

The diploid genome of a sexually reproducing species' cell has different alleles of the same locus. If the cell replicates itself by passing one chromatid to each daughter cell which then duplicate that to make a diploid genome, the resulting cells will not have the same DNA as the original one since each of the daughter cells will have inherited only one of the available alleles. They will then make an exact copy of the DNA they have inherited and become diploid but with a new genome, one that did not exist in their parent. This is not good since the cells of an organism need to have the same genome in order to function in the same way.

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Yes.. it would also lead to homozygosity. –  biogirl Sep 9 '13 at 16:52
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The biggest problem is this: if you have only one copy of the DNA how is it going to divide it between the two cells so that both have a complete copy?

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