Learn About Cell Division
2.5 Cell Division
2.5.5 Explain how mitosis produces two genetically identical nuclei.
2.5.5 Explain how mitosis produces two genetically identical nuclei (3).
Explain means to give a detailed account of causes, reasons or mechanisms.
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The process of cell division produces genetically identical daughter cells.
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Conservation of chromosome number. The chromosome number in each of the daughter cells is the same as that of the original parental cell
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During the S-phase, each chromosome is copied exactly. The two copies of each chromosome are held together by a protein structure called a centromere.
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Therefore just prior to the beginning of the phases of mitosis there is actually double the number of chromosomes present in a cell.
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Each chromosome in this state is represented by a pair of sister chromatids. These give the now classic cross image of the DNA (see image below)
This pair of sister chromatids image was taken during one of the phases of mitosis.
The two sister chromatids are held together at the centromere
The arms of the chromatids are visible because of a condensation of the molecule called super coiling.
This condenses the molecule some x 15,000 times of its original length The pairs of sister chromatids is a non-random organisation. The position of genes is predicable within the structure seen here. Also there is a unique shape to each of the chromosomes.
Mitosis makes sure that each cell obtains a copy of each of the chromosomes in the parental cell.
However, it is the process of DNA replication during the S-phase that actually copies each DNA molecules to make mitosis possible.