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Mitosis

Mitosis in an animal cell (phases ordered anti-clockwise). Mitosis divides the chromosomes in a cell nucleus. Onion (Allium) cells in different phases of the cell cycle enlarged 800 diameters. a. non-dividing cells b. nuclei preparing for division (spireme-stage) c. dividing cells showing mitotic figures e. pair of daughter-cells shortly after division Mitosis is a part of the cell cycle in which chromosomes in a cell nucleus are separated into two identical sets of chromosomes, and each set ends up in its own nucleus. In general, mitosis (division of the nucleus) is often accompanied or followed by cytokinesis, which divides the cytoplasm, organelles and cell membrane into two new cells containing roughly equal shares of these cellular components. Mitosis and cytokinesis together define the mitotic (M) phase of an animal cell cycle—the division of the mother cell into two daughter cells, genetically identical to each other and to their parent cell.The process of mitosis is divided into stages corresponding to the completion of one set of activities and the start of the next. These stages are prophase, prometaphase, metaphase, anaphase, and telophase. During mitosis, the chromosomes, which have already duplicated, condense and attach to spindle fibers that pull one copy of each chromosome to opposite sides of the cell. The result is two genetically identical daughter nuclei. The rest of the cell may then continue to divide by cytokinesis to produce two daughter cells. Producing three or more daughter cells instead of normal two is a mitotic error called tripolar mitosis or multipolar mitosis (direct cell triplication / multiplication). Other errors during mitosis can induce apoptosis (programmed cell death) or cause mutations. Certain types of cancer can arise from such mutations.Mitosis occurs only in eukaryotic cells and the process varies in different organisms. For example, animals undergo an "open" mitosis, where the nuclear envelope breaks down before the chromosomes separate, while fungi undergo a "closed" mitosis, where chromosomes divide within an intact cell nucleus. Furthermore, most animal cells undergo a shape change, known as mitotic cell rounding, to adopt a near spherical morphology at the start of mitosis. Prokaryotic cells, which lack a nucleus, divide by a different process called binary fission. ^ Carter, J. Stein (2014-01-14). "Mitosis". biology.clc.uc.edu.  ^ "Cell Division: Stages of Mitosis | Learn Science at Scitable". www.nature.com. Retrieved 2015-11-16.  ^ Cite error: The named reference Maton1997 was invoked but never defined (see the help page). ^ Kalatova, B.; Jesenska, R.; Hlinka, D.; Dudas, M. (2015). "Tripolar mitosis in human cells and embryos: Occurrence, pathophysiology and medical implications". Acta Histochemica 117 (1): 111–125. doi:10.1016/j.acthis.2014.11.009. PMID 25554607.  ^ Kops, G. J.; Weaver, B. A.; Cleveland, D. W. (October 2005). "On the road to cancer: Aneuploidy and the mitotic checkpoint". Nature Reviews Cancer 5 (10): 773–785. doi:10.1038/nrc1714. PMID 16195750.  ^ Cite error: The named reference Raikov1994 was invoked but never defined (see the help page). ^ Cite error: The named reference DeSouza2007 was invoked but never defined (see the help page).
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