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Mitosis is a part of the cell cycle in which chromosomes in a cell nucleus are separated into two identical sets of chromosomes, each in its own nucleus. In general, mitosis (division of the nucleus) is often 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 cell may then 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. == Discovery == German zoologist Otto Bütschli might have claimed the discovery of the process presently known as "mitosis",〔Fokin, S. I. (2013). (Otto Bütschli (1848–1920): Where we will genuflect? ) ''Protistology'', 8 (1), 22–35.〕 a term coined by Walther Flemming in 1882. Mitosis was discovered in frog, rabbit, and cat cornea cells in 1873 and described for the first time by the Polish histologist Wacław Mayzel in 1875. The term is derived from the Greek word μίτος ''mitos'' "warp thread".〔(【引用サイトリンク】url=http://www.etymonline.com/index.php?term=mitosis&allowed_in_frame=0 )〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「mitosis」の詳細全文を読む スポンサード リンク
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