Mitosis

Mitosis (/maɪˈtoʊsɪs/) is a part of the cell cycle in which replicated chromosomes are separated into two new nuclei. Cell division by mitosis is an equational division which gives rise to genetically identical cells in which the total number of chromosomes is maintained.^[1] Mitosis is preceded by the S phase of interphase (during which DNA replication occurs) and is followed by telophase and cytokinesis, which divide the cytoplasm, organelles, and cell membrane of one cell into two new cells containing roughly equal shares of these cellular components.^[2] The different stages of mitosis altogether define the mitotic phase (M phase) of a cell cycle—the division of the mother cell into two daughter cells genetically identical to each other.^[3]

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 preprophase (specific to plant cells), prophase, prometaphase, metaphase, anaphase, and telophase. During mitosis, the chromosomes, which have already duplicated during interphase, condense and attach to spindle fibers that pull one copy of each chromosome to opposite sides of the cell.^[4] 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.^[5] The different phases of mitosis can be visualized in real time, using live cell imaging.^[6]

An error in mitosis can result in the production of three or more daughter cells instead of the normal two. This is called tripolar mitosis and multipolar mitosis, respectively. These errors can be the cause of non-viable embryos that fail to implant.^[7] Other errors during mitosis can induce mitotic catastrophe, apoptosis (programmed cell death) or cause mutations. Certain types of cancers can arise from such mutations.^[8]

Mitosis occurs only in eukaryotic cells and varies between organisms.^[9] For example, animal cells generally undergo an open mitosis, where the nuclear envelope breaks down before the chromosomes separate, whereas fungal cells generally undergo a closed mitosis, where chromosomes divide within an intact cell nucleus.^[10][11] Most animal cells undergo a shape change, known as mitotic cell rounding, to adopt a near spherical morphology at the start of mitosis. Most human cells are produced by mitotic cell division. Important exceptions include the gametes – sperm and egg cells – which are produced by meiosis. Prokaryotes, bacteria and archaea which lack a true nucleus, divide by a different process called binary fission.^[12]