CELL DIVISION is the process by which a parent cell divides into two or more daughter cells. Cell division usually occurs as part of a larger cell cycle . In eukaryotes , there are two distinct types of cell division: a vegetative division, whereby each daughter cell is genetically identical to the parent cell (mitosis ), and a reproductive cell division, whereby the number of chromosomes in the daughter cells is reduced by half to produce haploid gametes (meiosis ). Meiosis results in four haploid daughter cells by undergoing one round of DNA replication followed by two divisions. Homologous chromosomes are separated in the first division, and sister chromatids are separated in the second division. Both of these cell division cycles are used in the process of sexual reproduction at some point in their life cycle. Both are believed to be present in the last eukaryotic common ancestor. Prokaryotes undergo a vegetative cell division known as binary fission , where their genetic material is segregated equally into two daughter cells. All cell divisions, regardless of organism, are preceded by a single round of DNA replication .
For simple unicellular organisms such as the amoeba , one cell division is equivalent to reproduction – an entire new organism is created. On a larger scale, mitotic cell division can create progeny from multicellular organisms, such as plants that grow from cuttings. Mitotic cell division enables sexually reproducing organisms to develop from the one-celled zygote , which itself was produced by meiotic cell division from gametes . After growth, cell division by mitosis allows for continual construction and repair of the organism. The human body experiences about 10 quadrillion cell divisions in a lifetime.
The primary concern of cell division is the maintenance of the original cell's genome . Before division can occur, the genomic information that is stored in chromosomes must be replicated, and the duplicated genome must be separated cleanly between cells. A great deal of cellular infrastructure is involved in keeping genomic information consistent between generations.
* 1 Phases of cell division
* 2 Variants * 3 Degradation * 4 See also * 5 Notes * 6 References * 7 Further reading * 8 External links
PHASES OF CELL DIVISION
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Interphase is the process a cell must go through before mitosis, meiosis, and cytokinesis. Interphase consists of four main stages: G1, S, and G2. G1 is a time of growth for the cell. If the cell does not progress through G1, the cell then enters a stage called G0. In G0, cells are still living but they are put on hold. The cells may later be called back into interphase if needed at a later time. There are checkpoints during interphase that allow the cell to be either progressed or denied further development. In S phase, the chromosomes are replicated in order for the genetic content to be maintained. During G2, the cell undergoes the final stages of growth before it enters the M phase. The M phase, can be either mitosis or meiosis depending on the type of cell. Germ cells undergo meiosis, while somatic cells will undergo mitosis. After the cell proceeds through successfully through the M phase, it may then undergo cell division through cytokinesis. The control of each checkpoint is controlled by cyclin and cyclin dependent kinases. The progression of interphase is the result of the increased amount of cyc