In biology, fission occurs when a cell (or body, population, or species) divides into two or more parts and the regeneration of those parts into separate cells (bodies, populations, or species). Binary fission produces two separate cells, populations, species, etc., whereas multiple fission produces more than two cells, populations, species, etc.
Binary fission of prokaryotes
Prokaryotic fission, which is binary fission, is a form of asexual reproduction and cell division used by all prokaryotes, (bacteria and archaebacteria), and some organelles within eukaryotic organisms (e.g., mitochondria). This process results in the reproduction of a living prokaryotic cell (or organelle) by division into two parts that each have the potential to grow to the size of the original cell (or organelle). This type of division takes place without the formation of spindles. The single DNA molecule first replicates, then attaches each copy to a different part of the cell membrane. When the cell begins to pull apart, the replicated and original chromosomes are separated. The consequence of this asexual method of reproduction is that all the cells are genetically identical, meaning that they have the same genetic material (barring random mutations).
Process of fission
The process of reproduction in a bacterial cell occurs through binary fission. In eukaryotic cells, asexual reproduction occurs through the more complex process of mitosis. The process of binary fission in bacteria involves:
- Replication of the circular DNA molecule inside the cell.
- Replicated DNA move to either poles of the cell.
- The cell lengthens.
- The equatorial plate of the cell constricts and separates the plasma membrane so each new cell has exactly the same genetic material.
This process is rapid and typically takes around 20 minutes at room temperature, meaning a single cell can produce millions of descendants in the space of a few hours. Note that not all bacterial cells undergo binary fission in 20 minutes; it can sometimes take as long as 24 hours.
Multiple fission of protists
Multiple fission at the cellular level occurs in many protists, e.g. sporozoans and algae. The nucleus of the parent cell divides several times by mitosis, producing several nuclei. The cytoplasm then separates, creating multiple daughter cells.
In apicomplexans, multiple fission, or schizogony, is manifested either as merogony, sporogony or gametogony. Merogony results in merozoites, which are multiple daughter cells, that originate within the same cell membrane, sporogony results in sporozoites, and gametogony results in microgametes.
Fragmentation in multicellular or colonial organisms is a form of asexual reproduction or cloning where an organism is split into fragments. Each of these fragments develop into mature, fully grown individuals that are clones of the original organism. In echinoderms, this method of reproduction is usually known as fissiparity.
- Cytokinesis, cell division in eukaryotes
- Fission-fusion society, a type of social organization that is notable among primates
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