Fission, in biology, is the division of a single entity into two or more parts and the regeneration of those parts to separate entities resembling the original. The object experiencing fission is usually a cell, but the term may also refer to how

organism In biology, an organism () is any living system that functions as an individual entity. All organisms are composed of cells ( cell theory). Organisms are classified by taxonomy into groups such as multicellular animals, plants, and fu ...

s, bodies,

population Population typically refers to the number of people in a single area, whether it be a city or town, region, country, continent, or the world. Governments typically quantify the size of the resident population within their jurisdiction usi ...

s, or

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriat ...

split into discrete parts. The fission may be ''binary fission'', in which a single organism produces two parts, or ''multiple fission'', in which a single entity produces multiple parts.

Binary fission

Organisms in the domains of

Archaea Archaea ( ; singular archaeon ) is a domain of single-celled organisms. These microorganisms lack cell nuclei and are therefore prokaryotes. Archaea were initially classified as bacteria, receiving the name archaebacteria (in the Archaeba ...

and

Bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were am ...

reproduce with binary fission. This form of

asexual reproduction Asexual reproduction is a type of reproduction that does not involve the fusion of gametes or change in the number of chromosomes. The offspring that arise by asexual reproduction from either unicellular or multicellular organisms inherit the ...

and

cell division Cell division is the process by which a parent cell divides into two daughter cells. Cell division usually occurs as part of a larger cell cycle in which the cell grows and replicates its chromosome(s) before dividing. In eukaryotes, there ...

is also used by some

organelle In cell biology, an organelle is a specialized subunit, usually within a cell, that has a specific function. The name ''organelle'' comes from the idea that these structures are parts of cells, as organs are to the body, hence ''organelle,'' th ...

s within eukaryotic organisms (e.g.,

mitochondria A mitochondrion (; ) is an organelle found in the cells of most Eukaryotes, such as animals, plants and fungi. Mitochondria have a double membrane structure and use aerobic respiration to generate adenosine triphosphate (ATP), which is used ...

). Binary fission results in the reproduction of a living prokaryotic cell (or organelle) by dividing the cell into two parts, each with the potential to grow to the size of the original.

Fission of prokaryotes

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

chromosome A chromosome is a long DNA molecule with part or all of the genetic material of an organism. In most chromosomes the very long thin DNA fibers are coated with packaging proteins; in eukaryotic cells the most important of these proteins ar ...

s 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

mutation In biology, a mutation is an alteration in the nucleic acid sequence of the genome of an organism, virus, or extrachromosomal DNA. Viral genomes contain either DNA or RNA. Mutations result from errors during DNA or viral replication, m ...

s). Unlike the processes of mitosis and

meiosis Meiosis (; , since it is a reductional division) is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, such as sperm or egg cells. It involves two rounds of division that ultimately ...

used by eukaryotic cells, binary fission takes place without the formation of a spindle apparatus on the cell. Like in mitosis (and unlike in meiosis), the parental identity is lost.

Process of FtsZ-dependent fission

FtsZ is homologous to

β-tubulin Tubulin in molecular biology can refer either to the tubulin protein superfamily of globular proteins, or one of the member proteins of that superfamily. α- and β-tubulins polymerize into microtubules, a major component of the eukaryotic cytosk ...

, the building block of the microtubule cytoskeleton used during mitosis in eukaryotes. FtsZ is thought to be the first protein to localize to the site of future division in bacteria, and it assembles into a Z ring, anchored by FtsZ-binding proteins and defines the division plane between the two daughter cells.

MinC The MinC protein is one of three proteins in the Min system encoded by the ''minB'' operon and which is required to generate pole to pole oscillations prior to bacterial cell division as a means of specifying the midzone of the cell. This functio ...

and MinD function together as division inhibitors, blocking formation of the FtsZ ring. MinE stops the MinCD activity midcell, allowing FtsZ to take over for binary fission. More specifically, the following steps occur: # The bacterium before binary fission is when the DNA is tightly coiled. # The DNA of the bacterium has uncoiled and duplicated. # The DNA is pulled to the separate poles of the bacterium as it increases the size to prepare for splitting. # The growth of a new cell wall begins to separate the bacterium (triggered by FtsZ polymerization and "Z-ring" formation) # The new cell wall ( septum) fully develops, resulting in the complete split of the bacterium. # The new daughter cells have tightly coiled DNA rods,

ribosome Ribosomes ( ) are macromolecular machines, found within all cells, that perform biological protein synthesis (mRNA translation). Ribosomes link amino acids together in the order specified by the codons of messenger RNA (mRNA) molecules to fo ...

s, and plasmids; these are now brand-new organisms. Studies of bacteria made to not produce a cell wall, called L-form bacteria, shows that FtsZ requires a

cell wall A cell wall is a structural layer surrounding some types of cells, just outside the cell membrane. It can be tough, flexible, and sometimes rigid. It provides the cell with both structural support and protection, and also acts as a filtering mec ...

to work. Little is known about how bacteria that naturally don't grow a cell wall divides, but it is thought to resemble the L-form's

budding Budding or blastogenesis is a type of asexual reproduction in which a new organism develops from an outgrowth or bud due to cell division at one particular site. For example, the small bulb-like projection coming out from the yeast cell is kno ...

-like division process of extrusion and separation.

Speed of FtsZ-dependent Fission

Binary fission is generally rapid though its speed varies between species. For '' E. coli'', cells typically divide about every 20 minutes at 37 °C. Because the new cells will, in turn, undergo binary fission on their own, the time binary fission requires is also the time the bacterial culture requires to double in the number of cells it contains. This time period can, therefore, be referred to as the doubling time. Some species other than ''E. coli'' may have faster or slower doubling times: some strains of '' Mycobacterium tuberculosis'' may have doubling times of nearly 100 hours. Bacterial growth is limited by factors including nutrient availability and available space, so binary fission occurs at much lower rates in bacterial cultures once they enter the stationary phase of growth.

In archaea

Thermoproteota (formerly Crenarchaeota) possess neither a cell wall nor the FtsZ mechanism. They use a primitive version of the eukaryotic ESCRT-III system (also known as ''Cdv'') to manipulate the membrane into separating, specifically by coming into the middle of the two soon-to-be daughter cells. " Euryarchaeota" use FtsZ like bacteria do.

Fission of organelles

Some organelles in eukaryotic cells reproduce using binary fission.

Mitochondrial fission Mitochondrial fission is the process where mitochondria divide or segregate into two separate mitochondrial organelles. Mitochondrial fission is counteracted by the process of mitochondrial fusion, whereby two separate mitochondria can fuse toget ...

occurs frequently within the cell, even when the cell is not actively undergoing mitosis, and is necessary to regulate the cell's

metabolism Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run ...

. All chloroplasts and some mitochrondria (not in animals), both organelles derived from endosymbiosis of bacteria, also use FtsZ in a bacteria-like fashion.

Types of binary

Binary fission in organisms can occur in four ways, irregular, longitudinal, transverse, oblique.i.e.left oblique & right oblique # Irregular: In this fission,

cytokinesis Cytokinesis () is the part of the cell division process during which the cytoplasm of a single eukaryotic cell divides into two daughter cells. Cytoplasmic division begins during or after the late stages of nuclear division in mitosis and mei ...

may take place along any plane but it is always perpendicular to the plane of karyokinesis (nuclear division). e.g. amoeba # Longitudinal: Here cytokinesis takes place along the longitudinal axis. e.g. in

flagellate A flagellate is a cell or organism with one or more whip-like appendages called flagella. The word ''flagellate'' also describes a particular construction (or level of organization) characteristic of many prokaryotes and eukaryotes and thei ...

s like '' Euglena''. # Transverse: Here cytokinesis takes place along the transverse axis. e.g. in

ciliate The ciliates are a group of alveolates characterized by the presence of hair-like organelles called cilia, which are identical in structure to eukaryotic flagella, but are in general shorter and present in much larger numbers, with a differen ...

protozoa Protozoa (singular: protozoan or protozoon; alternative plural: protozoans) are a group of single-celled eukaryotes, either free-living or parasitic, that feed on organic matter such as other microorganisms or organic tissues and debris. Histo ...

ns like '' Paramecium''. # Oblique: In this type of binary fission cytokinesis occurs obliquely. Example '' Ceratium'' Binary fission means "division into two". It is the simplest and most common method of asexual reproduction.

Multiple fission

Fission of protists

Multiple fission at the cellular level occurs in many protistists, e.g. sporozoans and

algae Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular micr ...

. The

nucleus Nucleus ( : nuclei) is a Latin word for the seed inside a fruit. It most often refers to: * Atomic nucleus, the very dense central region of an atom *Cell nucleus, a central organelle of a eukaryotic cell, containing most of the cell's DNA Nucl ...

of the parent cell divides several times by

amitosis Amitosis ('' a-'' + ''mitosis''), also called karyostenosis or direct cell division or binary fission, is cell proliferation that does not occur by mitosis, the mechanism usually identified as essential for cell division in eukaryotes. The polyploi ...

, producing several nuclei. The cytoplasm then separates, creating multiple daughter cells. Some parasitic, single-celled organisms undergo a multiple fission-like process to produce numerous daughter cells from a single parent cell. Isolates of the human parasite ''

Blastocystis hominis ''Blastocystis'' is a genus of single-celled heterokont parasites belonging to a group of organisms that are known as the Stramenopiles (also called Heterokonts) that includes algae, diatoms, and water molds. Blastocystis consists of several ...

'' were observed to begin such a process within 4 to 6 days. Cells of the fish parasite '' Trypanosoma borreli'' have also been observed participating in both binary and multiple fission.

Fission of apicomplexans

In the apicomplexans, a phylum of parasitic protists, multiple fission, or schizogony, is manifested either as merogony,

sporogony Apicomplexans, a group of intracellular parasites, have life cycle stages that allow them to survive the wide variety of environments they are exposed to during their complex life cycle. Each stage in the life cycle of an apicomplexan organism is ...

gametogony Apicomplexans, a group of intracellular parasites, have life cycle stages that allow them to survive the wide variety of environments they are exposed to during their complex life cycle. Each stage in the life cycle of an apicomplexan organism is ...

. Merogony results in

merozoite Apicomplexans, a group of intracellular parasites, have life cycle stages that allow them to survive the wide variety of environments they are exposed to during their complex life cycle. Each stage in the life cycle of an apicomplexan organism i ...

s, which are multiple daughter cells, that originate within the same cell membrane, sporogony results in sporozoites, and gametogony results in micro

gamete A gamete (; , ultimately ) is a haploid cell that fuses with another haploid cell during fertilization in organisms that reproduce sexually. Gametes are an organism's reproductive cells, also referred to as sex cells. In species that produce ...

Fission of green algae

Green algae can divide into more than two daughter cells. The exact number of daughter cells depends on the species of algae and is an effect of temperature and light.

Multiple fission of bacteria

Most species of bacteria primarily undergo binary reproduction. Some species and groups of bacteria may undergo multiple fission as well, sometimes beginning or ending with the production of

spore In biology, a spore is a unit of sexual or asexual reproduction that may be adapted for dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores form part of the life cycles of many plants, algae, ...

s. The species '' Metabacterium polyspora'', a symbiont of

guinea pig The guinea pig or domestic guinea pig (''Cavia porcellus''), also known as the cavy or domestic cavy (), is a species of rodent belonging to the genus '' Cavia'' in the family Caviidae. Breeders tend to use the word ''cavy'' to describe the ...

s, has been found to produce multiple endospores in each division. Some species of

cyanobacteria Cyanobacteria (), also known as Cyanophyta, are a phylum of gram-negative bacteria that obtain energy via photosynthesis. The name ''cyanobacteria'' refers to their color (), which similarly forms the basis of cyanobacteria's common name, bl ...

have also been found to reproduce through multiple fission.

Plasmotomy

Some protozoans reproduce by yet another mechanism of fission called as plasmotomy. In this type of fission, a multinucleate adult parent undergoes cytokinesis to form two multinucleate (or coenocytic) daughter cells. The daughter cells so produced undergo further mitosis. ''

Opalina ''Opalina'' is a genus of parasitic heterokonts found in the intestines of frogs and toads. They lack mouths and contractile vacuoles, they are covered with nearly equal flagelliform cilia, and they have numerous nuclei, all similar. All the spe ...

'' and '' Pelomyxa'' reproduce in this way.

Clonal fragmentation

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

echinoderm An echinoderm () is any member of the phylum Echinodermata (). The adults are recognisable by their (usually five-point) radial symmetry, and include starfish, brittle stars, sea urchins, sand dollars, and sea cucumbers, as well as the ...

s, this method of reproduction is usually known as fissiparity.

Population fission

Any splitting of a single population of individuals into discrete parts may be considered fission. A population may undergo fission process for a variety of reasons, including migration or geographic isolation. Since the fission leads to genetic variance in the newly isolated, smaller populations, population fission is a precursor to speciation.

References

{{Reflist Asexual reproduction Cell cycle