In cell biology, mitosis is a part of the cell cycle when replicated chromosomes are separated into two new nuclei. Cell division gives rise to genetically identical cells in which the number of chromosomes is maintained. In general, mitosis (division of the nucleus) is preceded by the S stage of interphase (during which the DNA is replicated) and 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.
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 the 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 and the foreskin
Placing human tissue under tension causes the cells to sense the need for more tissue. The cells then start to divide and create more tissue identical to the original tissue. The additional tissue results in tissue expansion, which is a recognized medical practice. Tissue may be placed under tension by applying traction, stretching skin manually, or by tugging with a device.
- Men who have a narrow tight foreskin or phimosis may stretch the narrow part of their foreskin laterally to cause mitosis, which results in a wider, retractable foreskin.
- Men who have been circumcised may stretch their residual shaft skin longitudinally to lengthen it until it takes the shape of a foreskin.
- Intact men who wish to have a longer foreskin may stretch their foreskin longitudinally to make it longer.
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