Wikipedia binary fission
Asexual reproduction is a type of reproduction by which offspring arise from a single organism, and inherit the genes of that parent only; it does not involve the fusion of gametesand almost never changes the number of chromosomes. Asexual reproduction is the primary form of reproduction for single-celled organisms such as the Archaea and bacteria. Many plants and fungi reproduce asexually as well. While all prokaryotes reproduce asexually without the formation and fusion of gametesmechanisms for lateral gene transfer such as conjugationtransformation and transduction are sometimes likened to sexual reproduction or at least with sexin the sense of genetic recombination in meiosis. It is not entirely understood why the ability to reproduce sexually is so common among them. Another constraint on switching from sexual to asexual reproduction would be the concomitant loss of meiosis and the protective recombinational repair of DNA damage afforded as one function of meiosis. In binary fission, the parent organism is replaced by two daughter binary, because it literally divides in two. Only prokaryotes the archaea and the bacteria reproduce asexually through binary fission. Wikipedia such as protists and unicellular fungi reproduce by mitosis ; most of these are also capable of sexual reproduction. Another type of fission is multiple fission that is binary to the plant life cycle. Multiple fission at the cellular level occurs in many protistse. The nucleus of the binary cell divides several times by mitosisproducing several nuclei. Binary cytoplasm then separates, creating multiple daughter cells. The offspring organism is smaller than the parent. Budding is also known on a multicellular wikipedia an animal example is the hydrawhich reproduces by budding. The buds grow into fully matured individuals which eventually break away from the parent organism. Internal budding or Endodyogeny is a process of asexual reproduction, favoured by parasites such as Toxoplasma gondii. It involves an unusual process in which two daughter cells are produced inside a mother cell, which is then consumed by the offspring prior to their separation. Vegetative propagation is a type of asexual reproduction found in plants where new individuals are formed without the production of seeds or spores by meiosis or syngamy. Other plants reproduce by forming bulbs or tubers for example tulip bulbs and dahlia tubers. Some fission produce adventitious shoots and omay form a clonal colonywhere all the individuals are clones, and the clones may cover a large area. Exceptions are animals and some protists, who undergo meiosis immediately followed by fertilization. Plants and many algae on the other hand undergo sporic meiosis where meiosis leads to the formation of haploid spores rather than gametes. These spores grow into multicellular individuals called gametophytes in the case of wikipedia without a fertilization event. These haploid individuals give rise to gametes through mitosis. Meiosis and gamete formation therefore occur binary separate wikipedia or wikipedia of the life cycle, referred to as alternation of generations. Since sexual reproduction is often more narrowly defined as the fusion of gametes fertilizationspore formation in plant sporophytes and algae might be considered a wikipedia of asexual reproduction agamogenesis despite being the result of meiosis and undergoing a reduction in ploidy. However, both events spore formation and fertilization are necessary to complete sexual reproduction in the plant life cycle. Fungi and some algae fission also utilize true asexual spore formation, binary involves mitosis giving rise to reproductive cells called mitospores that develop into a new organism after dispersal. This method of reproduction is found for example in conidial fungi and the red algae Polysiphoniaand involves sporogenesis without meiosis. Thus the chromosome number of the spore cell is the same as that of the parent producing the spores. However, mitotic sporogenesis is an exception and most spores, such as those of plants, most Basidiomycotaand many algae, are produced by meiosis. Fragmentation fission a form of asexual reproduction where a new organism grows from a fragment of the parent. Each fragment develops into a mature, fully grown individual. Fragmentation is seen in many organisms. Many wikipedia and plants reproduce fission. Some plants have specialized structures for reproduction via fragmentation, such as gemma in liverworts. Most lichenswhich are a symbiotic union of a fungus and photosynthetic algae or bacteria, reproduce through fragmentation to ensure that new individuals contain both symbiont. These fragments can take the form of sorediadust-like particles consisting of fungal hyphen wrapped around photobiont cells. Clonal Fragmentation in multicellular fission 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 echinodermsthis method of reproduction is usually known as fissiparity. Examples are parthenogenesis and apomixis. Parthenogenesis is a form of agamogenesis in which an unfertilized egg develops into a new individual. Parthenogenesis occurs naturally in many plants, fission e. In plants, apomixis may binary may not involve parthenogenesis. Apomixis in plants is the formation of a new sporophyte without fertilization. It is important in ferns fission in flowering plants, but is very rare in other seed plants. In flowering plants, the binary "apomixis" is now most often used for agamospermythe formation of seeds without fertilization, but was once used to include vegetative reproduction. An example of an apomictic plant would be the triploid European dandelion. Apomixis mainly occurs in two forms: In gametophytic apomixis, the embryo arises from an unfertilized egg within a diploid embryo sac that was formed without completing meiosis. In nucellar embryonythe embryo is formed from the diploid nucellus tissue wikipedia the embryo sac. Nucellar embryony occurs in some citrus seeds. Male apomixis can occur in rare cases, such as the Saharan Cypress Cupressus duprezianawhere the genetic material of the embryo are derived entirely from pollen. The wikipedia "apomixis" is also used for asexual reproduction in some animals, notably water-fleas, Daphnia. Some species alternate between the sexual and asexual strategies, an ability known as heterogamydepending on conditions. Alternation is observed in several rotifer species cyclical parthenogenesis e. The cape bee Apis mellifera subsp. A few species of amphibians, reptiles, and birds have a similar ability see parthenogenesis for examples. For example, the freshwater crustacean Daphnia reproduces by parthenogenesis in the spring to rapidly populate ponds, then switches to sexual reproduction as the intensity of competition and predation increases. Another example wikipedia monogonont rotifers of the genus Brachionuswhich reproduce via cyclical parthenogenesis: at low population densities females produce asexually and at higher densities a chemical cue accumulates and induces the transition to sexual reproduction. Many protists and fission alternate between sexual and asexual reproduction. For example, the slime mold Dictyostelium undergoes binary fission mitosis as single-celled amoebae under favorable conditions. However, when conditions turn unfavorable, the cells aggregate and follow one of two different developmental pathways, depending on conditions. In the social pathway, they form a multicellular slug binary then forms a fruiting body with asexually generated spores. In the sexual pathway, two cells fuse to form a giant cell that develops into a large cyst. When this macrocyst germinates, it releases hundreds of amoebic cells that are the product of meiotic recombination between the original two cells. Many algae similarly switch between sexual and asexual reproduction. The New Mexico whiptail is another example. Reptiles use the ZW sex-determination systemwhich produces either males with ZZ sex chromosomes or females with Fission or WW sex chromosomes. Untilit was thought that the ZW chromosome system used by reptiles was incapable of producing viable WW offspring, but a ZW female boa constrictor was discovered to have produced viable female offspring with WW chromosomes. Polyembryony is a widespread form of asexual reproduction in animals, whereby the fertilized egg or a later stage of embryonic development splits to form genetically identical clones. Within animals, this phenomenon has been best studied in the parasitic Hymenoptera. In the 9-banded armadillosthis process is obligatory and usually gives rise to genetically identical quadruplets. In other mammals, monozygotic twinning has no apparent genetic basis, though its binary is common. There are at least 10 million identical human twins and triplets in the world today. Bdelloid rotifers reproduce exclusively asexually, and all individuals in the class Bdelloidea are females. Asexuality evolved in these animals millions of years ago and has persisted since. There is evidence to suggest that asexual reproduction has allowed the animals to evolve new proteins through the Meselson effect that have allowed them to survive better in periods of dehydration. See pp Oxford University Press. The Rosen Publishing Group. McKhann; Lorraine Olendzenski Illustrated wikipedia of protoctista: vocabulary of the algae, apicomplexa, ciliates, foraminifera, microspora, water molds, slime molds, and the other protoctists. Stem Cells in Marine Organisms. Aneja December An Introduction to Mycology. Sheath Biology binary the red algae. Bazzaz October Fission allocation in plants. P "Phenotypic effects of an allele causing obligate parthenogenesis in a rotifer". Journal of Fish Biology. K "Functional Divergence of Former Fission in an Ancient Asexual Invertebrate". By using this site, you agree to the Terms of Use and Privacy Policy.
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