What Happens In Each Phase Of Mitosis

What are the steps of mitosis? What happens in each?

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The cell cycle of a somatic cell consists of interphase and mitosis/cytokinesis.  During interphase, which occurs prior to mitosis, there are 3 phases: G1, S, and G2.  During the G phases the cell grows in size and organelles duplicate.  During the S phase, a duplicate copy of each chromosome is synthesized.  This produces an identical sister chromatid for all 46 chromosomes.  The X shaped chromosomes that form when the DNA condenses are paired sister chromatids.  Each half of the X is one sister chromatid.

After interphase is complete, mitosis can begin.  The first step is prophase.  During prophase, the nuclear envelope surrounding the DNA starts to disappear and the DNA condenses into chromosomes.  The 46 chromosomes each consist of 2 identical sister chromatids.  The centrioles move to opposite poles of the parent cell.

The second step of mitosis is metaphase.  During metaphase all of the chromosomes line up in the middle of the parent cell.  The centrioles produce spindles that attach to the centromere of each sister chromatid.

The third step of mitosis is anaphase.  During anaphase, the spindle fibers pull the identical sister chromatids to opposite sides (poles) of the parent cell.

The fourth and final step of mitosis is telophase.  During telophase, two nuclear envelopes reform around the separated DNA and the DNA de-condenses so that chromosomes are no longer visible.  One can also see that the plasma membrane begins to constrict between the newly formed nuclei.

Mitosis is then followed by cytokinesis where the two nuclei and the duplicated organelles are separated into 2 distinct daughter cells.  The cells are identical in terms of genetic content.

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