Mitosis is the process by which cells reproduce. It occurs during the M-phase of the cell cycle. At this point, each chromosome consists of two identical sister chromatids, which were formed by DNA replication during interphase. The sister chromatids are held together by a centromere. There are four stages of mitosis: prophase, metaphase, anaphase, and telophase.In early prophase, chromosomes start becoming shorter and fatter by supercoiling, which involves the linking together of N-terminal tails of nucleosomes to tightly condense the DNA. Also, spindle microtubules begin to grow.Next, in late prophase, spindle microtubules extend from the poles of the cell to the equator, encasing the nucleus. In metaphase, the nuclear membrane breaks down and the chromosomes move to the equator of the cell. The spindle microtubules attach to each centromere on opposite sides.In anaphase, the centromeres divide and sister chromatids separate. Through separation, chromatids can now be identified as genetically identical chromosomes. The chromosomes are then pulled by spindle microtubules to opposite poles of the cell.By early telophase, all chromosomes have reached the poles. There, nuclear membranes form around the chromosomes and spindle microtubules break down. In late telophase the chromosomes uncoil, making them no longer individually visible, in preparation for interphase.The cell then undergoes cytokinesis, meaning cell division, to form two cells with genetically identical nuclei. Cytokinesis marks the end of mitosis, which effectively produces two cells with genetically identical nuclei.
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