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Encyclopedia > Asexual reproduction
Asexual reproduction in liverworts: a caducuous phylloid germinating

Asexual reproduction is a form of reproduction which does not involve meiosis, ploidy reduction, or fertilization. Asexual reproduction only takes one parent. A more stringent definition is agamogenesis which refers to reproduction without the fusion of gametes. Asexual reproduction is the primary form of reproduction for single-celled organisms such the archaea, bacteria, and protists. Many plants and fungi reproduce asexually as well. While all prokaryotes reproduce asexually (without the formation and fusion of gametes), mechanisms for lateral gene transfer such as conjugation, transformation and transduction are sometimes likened to sexual reproduction.[1] Image File history File linksMetadata Download high resolution version (2048x1536, 389 KB) Summary A caducuous phylloid of a liverwort germinating Taken by J. Ziffer Berger Licensing I, the creator of this work, hereby release it into the public domain. ... Image File history File linksMetadata Download high resolution version (2048x1536, 389 KB) Summary A caducuous phylloid of a liverwort germinating Taken by J. Ziffer Berger Licensing I, the creator of this work, hereby release it into the public domain. ... Orders Need to be entered Liverworts are non-vascular plants in the Class Marchantiopsida, formerly known as the Hepaticae. ... For the figure of speech, see meiosis (figure of speech). ... Ploidy is the number of homologous sets of chromosomes in a biological cell. ... Categories: Biology stubs ... A gamete (from Ancient Greek γαμετης; translated gamete = wife, gametes = husband) is a cell that fuses with another gamete during fertilization (conception) in organisms that reproduce sexually. ... Cells in culture, stained for keratin (red) and DNA (green) The cell is the structural and functional unit of all living organisms, sometimes called the building blocks of life. ... Phyla Crenarchaeota Euryarchaeota Korarchaeota Nanoarchaeota ARMAN The Archaea (pronounced ) are a group of prokaryotic and single-celled microorganisms. ... Phyla Actinobacteria Aquificae Chlamydiae Bacteroidetes/Chlorobi Chloroflexi Chrysiogenetes Cyanobacteria Deferribacteres Deinococcus-Thermus Dictyoglomi Fibrobacteres/Acidobacteria Firmicutes Fusobacteria Gemmatimonadetes Lentisphaerae Nitrospirae Planctomycetes Proteobacteria Spirochaetes Thermodesulfobacteria Thermomicrobia Thermotogae Verrucomicrobia Bacteria (singular: bacterium) are unicellular microorganisms. ... Typical phyla Chromalveolata Chromista Heterokontophyta Haptophyta Cryptophyta (cryptomonads) Alveolata Dinoflagellata Apicomplexa Ciliophora (ciliates) Cabozoa Excavata Euglenozoa Percolozoa Metamonada Rhizaria Radiolaria Foraminifera Cercozoa Archaeplastida (in part) Rhodophyta (red algae) Glaucophyta (basal archaeplastids) Amoebozoa Choanozoa Many others; classification varies Protists (IPA: (RP); (GenAm)), Greek protiston -a meaning the (most) first of all... For other uses, see Plant (disambiguation). ... For the fictional character, see Fungus the Bogeyman. ... Prokaryotic bacteria cell structure Prokaryotes (IPA: //) are a group of organisms that lack a cell nucleus (= karyon), or any other membrane-bound organelles. ... Horizontal gene transfer is any process in which an organism transfers genetic material (i. ... Bacterial conjugation is the transfer of genetic material between bacteria through direct cell-to-cell contact. ... It has been suggested that this article or section be merged into Transfection. ... Transduction Transduction is the process by which bacterial DNA is moved from one bacterium to another by a virus. ... Sexual reproduction is a union that results in increasing genetic diversity of the offspring. ...


The lack of sexual reproduction is relatively rare among multicellular organisms, for reasons that are not completely understood. Current hypotheses suggest that, while asexual reproduction may have short term benefits when rapid population growth is important or in stable environments, sexual reproduction offers a net advantage by allowing more rapid generation of genetic diversity, allowing adaptation to changing environments.


Because asexual reproduction does not require the formation of gametes (often in separate individuals) and bringing them together for fertilization, it occurs much faster than sexual reproduction and requires less energy. Asexual lineages can increase their numbers rapidly because all members can reproduce viable offspring. In sexual populations with two genders, some of the individuals are male and cannot themselves produce offspring. This means that an asexual lineage will have roughly double the rate of population growth under ideal conditions when compared with a sexual population half composed of males. This is known as the two-fold cost of sex. Other advantages include the ability to reproduce without a partner in situations where the population density is low (such as for some desert lizards), reducing the chance of finding a mate, or during colonisation of isolated habitats such as oceanic islands, where a single (female) member of the species is enough to start a population. A gamete (from Ancient Greek γαμετης; translated gamete = wife, gametes = husband) is a cell that fuses with another gamete during fertilization (conception) in organisms that reproduce sexually. ... Categories: Biology stubs ... The evolution of sex is a major puzzle in modern evolutionary biology. ...


Another consequence of asexual reproduction, which may have both benefits and costs, is that offspring are typically genetically similar to their parent, with as broad a range as that individual receives from one parent. The lack of genetic recombination results in fewer genetic alternatives than with sexual reproduction. Many forms of asexual reproduction, for example budding or fragmentation, produce an exact replica of the parent. This genetic similarity may be beneficial if the genotype is well-suited to a stable environment, but disadvantageous if the environment is changing. For example, if a new predator or pathogen appears and a genotype is particularly defenseless against it, an asexual lineage is more likely to be completely wiped out by it. In contrast, a lineage that reproduces sexually has a higher probability of having more members survive due to the genetic recombination that produces a novel genotype in each individual. Similar arguments apply to changes in the physical environment. From an evolutionary standpoint, one could thus argue that asexual reproduction is inferior because it stifles the potential for change. However, there is also a significantly reduced chance of mutation or other complications that can result from the mixing of genes. A 2004 article in the journal Nature reported that the modern arbuscular mycorrhizas fungi, which reproduces asexually, is identical to fossil records dating back to the Ordovician period, 460 million years ago.[2] Genetic recombination is the process by which a strand of the genetic material (usually DNA; but can also be RNA) is broken and then joined to the end of a different DNA molecule. ... Look up replica in Wiktionary, the free dictionary. ... A pathogen (from Greek pathos, suffering/emotion, and gene, to give birth to), infectious agent, or more commonly germ, is a biological agent that causes disease or illness to its host. ... This article does not cite any references or sources. ... Genetic recombination is the process by which a strand of the genetic material (usually DNA; but can also be RNA) is broken and then joined to the end of a different DNA molecule. ... This article is about evolution in biology. ... For linguistic mutation, see Apophony. ... An Arbuscular mycorrhiza (plural mycorrhizae or mycorrhizas) is a type of mycorrhiza in which the fungus penetrates the cortical cells of the roots of a vascular plant. ... The Ordovician period is the second of the six (seven in North America) periods of the Paleozoic era. ...

Contents

Types of asexual reproduction

Binary fission

Main article: Binary fission

Many, but not all, single-celled organisms (unicellular), such as archaea, bacteria, and protists, reproduce asexually through binary fission. An exception to the rule are unicellular fungi such as fission yeast, unicellular algae such as Chlamydomonas, and ciliates and some other protists, which reproduce both sexually and asexually. Some single-celled organisms(unicellular) rely on one or more host organisms in order to reproduce, but most literally divide into two organisms. Binary fission Binary fission is the form of asexual reproduction in single-celled organisms by which one cell divides into two cells of the same size, used by most prokaryotes. ... Phyla Crenarchaeota Euryarchaeota Korarchaeota Nanoarchaeota ARMAN The Archaea (pronounced ) are a group of prokaryotic and single-celled microorganisms. ... Phyla Actinobacteria Aquificae Chlamydiae Bacteroidetes/Chlorobi Chloroflexi Chrysiogenetes Cyanobacteria Deferribacteres Deinococcus-Thermus Dictyoglomi Fibrobacteres/Acidobacteria Firmicutes Fusobacteria Gemmatimonadetes Lentisphaerae Nitrospirae Planctomycetes Proteobacteria Spirochaetes Thermodesulfobacteria Thermomicrobia Thermotogae Verrucomicrobia Bacteria (singular: bacterium) are unicellular microorganisms. ... Typical phyla Chromalveolata Chromista Heterokontophyta Haptophyta Cryptophyta (cryptomonads) Alveolata Dinoflagellata Apicomplexa Ciliophora (ciliates) Cabozoa Excavata Euglenozoa Percolozoa Metamonada Rhizaria Radiolaria Foraminifera Cercozoa Archaeplastida (in part) Rhodophyta (red algae) Glaucophyta (basal archaeplastids) Amoebozoa Choanozoa Many others; classification varies Protists (IPA: (RP); (GenAm)), Greek protiston -a meaning the (most) first of all... Binary fission Binary fission is the form of asexual reproduction in single-celled organisms by which one cell divides into two cells of the same size, used by most prokaryotes. ... Schizosaccharomyces pombe, also called fission yeast, is a species of yeast. ... Species See text. ... Classes Karyorelictea Heterotrichea Spirotrichea Litostomatea Phyllopharyngea Nassophorea Colpodea Prostomatea Oligohymenophorea Plagiopylea See text for subclasses. ... Typical phyla Chromalveolata Chromista Heterokontophyta Haptophyta Cryptophyta (cryptomonads) Alveolata Dinoflagellata Apicomplexa Ciliophora (ciliates) Cabozoa Excavata Euglenozoa Percolozoa Metamonada Rhizaria Radiolaria Foraminifera Cercozoa Archaeplastida (in part) Rhodophyta (red algae) Glaucophyta (basal archaeplastids) Amoebozoa Choanozoa Many others; classification varies Protists (IPA: (RP); (GenAm)), Greek protiston -a meaning the (most) first of all...


Budding

Main article: Budding

Some cells split via budding (for example baker's yeast), resulting in a smaller 'mother' cell and larger 'daughter' cell. Offspring is larger than parent. Budding is also known on a multicellular level. An animal example is hydra, which reproduces by budding. The buds grow into fully matured individuals which eventually break away from the parent organism. High magnification view of a budding yeast Budding is the formation of a new organism by the protrusion of part of another organism. ... High magnification view of a budding yeast Budding is the formation of a new organism by the protrusion of part of another organism. ... Binomial name Meyen ex E.C. Hansen Saccharomyces cerevisiae is a species of budding yeast. ... Species Hydra americana Hydra attenuata (or Hydra vulgaris) Hydra canadensis Hydra carnea Hydra cauliculata Hydra circumcincta Hydra hymanae Hydra littoralis Hydra magnipapillata Hydra minima Hydra oligactis Hydra oregona Hydra pseudoligactis Hydra rutgerensis Hydra utahensis Hydra viridis Hydra viridissima Hydra is a genus of simple, fresh-water animals possessing radial symmetry. ...


Vegetative reproduction

Vegetative reproduction is a type of asexual reproduction found in plants where new independent individuals are formed without the production of seeds or spores. Examples for vegetative reproduction include the formation of plantlets on specialized leaves (for example in kalanchoe), the growth of new plants out of rhizomes or stolons (for example in strawberry), or the formation of new bulbs (for example in tulips). The resulting plants form a clonal colony. Production of new individuals along a leaf margin of the air plant, Kalanchoë pinnata. ... Species See text. ... For other uses, see Rhizome (disambiguation). ... Silverweed (Argentina anserina) picture showing red stolons. ... For other uses, see Strawberry (disambiguation). ... For other uses, see Tulip (disambiguation). ... A clonal colony is a group of plants (or fungi) that have grown in a given location, all originating vegetatively, not sexually, from a given single ancestor. ...


Spore formation

Main article: Sporogenesis

Many multicellular organisms form spores during their biological life cycle in a process called sporogenesis. Exceptions are animals and some protists, who undergo gametic 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 plants) without a fertilization event. These haploid individuals give rise to gametes through mitosis. Meiosis and gamete formation therefore occur in separate generations or "phases" of the life cycle, referred to as alternation of generations. Since sexual reproduction is often more narrowly defined as the fusion of gametes (fertilization), spore formation in plant sporophytes and algae might be considered a form 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. Spores produced in a sporic life cycle. ... This article or section is in need of attention from an expert on the subject. ... A life cycle is a period involving one generation of an organism through means of reproduction, whether through asexual reproduction or sexual reproduction. ... In plants that undergo alternation of generations, a gametophyte is the structure, or phase of life, that contains only half of the total complement of chromosomes: The sporophyte produces spores, in a process called meiosis. ... A gamete (from Ancient Greek γαμετης; translated gamete = wife, gametes = husband) is a cell that fuses with another gamete during fertilization (conception) in organisms that reproduce sexually. ... Mitosis divides genetic information during cell division. ... Sporic or diplohaplontic life cycle. ... Categories: Biology stubs ... Young sporophytes of the common moss Tortula muralis. ... For the figure of speech, see meiosis (figure of speech). ... Ploidy is the number of homologous sets of chromosomes in a biological cell. ...


Fungi and some algae can also utilize true asexual spore formation, which 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 alga Polysiphonia, and 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 Basidiomycota, and many algae, are produced by meiosis. This article or section is in need of attention from an expert on the subject. ... Mitosis divides genetic information during cell division. ... Conidia Conidia are asexual spores of a fungus. ... Possible classes Florideophyceae Bangiophyceae Cyanidiophyceae Red algae (Rhodophyta, pronounced /ˈrəʊdə(ʊ)ˌfʌɪtə/) are a large group of mostly multicellular, marine algae, including many notable seaweeds. ... Subphyla/Classes Pucciniomycotina Ustilaginomycotina Agaricomycotina Incertae sedis (no phylum) Wallemiomycetes Entorrhizomycetes Basidiomycota is one of two large phyla, that together with the Ascomycota, comprise the subkingdom Dikarya, which were in general what were called the Higher Fungi within the Kingdom Fungi. ... For the figure of speech, see meiosis (figure of speech). ...


Fragmentation

Fragmentation is 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 such as animals (some annelid worms and starfish), fungi, and plants. Some plants have specialized structures for reproduction via fragmentation, such as gemmae in liverworts. Most lichens, which are a symbiotic union of a fungus and photosynthetic algae or bacteria, reproduce through fragmentation to ensure that new individuals contain both symbionts. These fragments can take the form of soredia, dust-like particles consisting of fungal hyphae wrapped around photobiont cells. For other uses, see fragmentation. ... A gemma is a small asexual reproductive structure in plants that detaches from the parent and develops into a new individual. ... Orders Jungermanniopsida Metzgeriales (simple thalloids) Haplomitriales (Calobryales) Jungermanniales (leafy liverworts) Marchantiopsida Sphaerocarpales (bottle liverworts) Marchantiales (complex thalloids) Monocleales Liverworts are a division of plants commonly called hepatics, Marchantiophyta or liverworts. ... For other uses, see Lichen (disambiguation). ... For other uses, see Symbiosis (disambiguation). ... Photosynthesis splits water to liberate O2 and fixes CO2 into sugar The leaf is the primary site of photosynthesis in plants. ...


Parthenogenesis

Main article: Parthenogenesis

Parthenogenesis is a form of agamogenesis in which an unfertilized egg develops into a new individual. Parthenogenesis occurs naturally in many plants, invertebrates (e.g. water fleas, aphids, stick insects, some bees and parasitic wasps), and vertebrates (e.g. some reptiles, amphibians, fish, very rarely birds). In plants, apomixis may or may not involve parthenogenesis. For the religious belief, see Virgin Birth of Jesus. ... It has been suggested that Parthenogenesis be merged into this article or section. ... Invertebrate is an English word that describes any animal without a spinal column. ... Ctenomorpha Chronus Ctenomorpha Chronus Medauroidea Extradentata Stick insects are members of the one of the two insect families Phasmatidae and Phylliidae. ... This article does not cite any references or sources. ... In botany, apomixis is asexual reproduction, without fertilization. ...


Agamogenesis

Main article: Agamogenesis

Agamogenesis is any form of reproduction that does not involve a male gamete. Examples are parthenogenesis and apomixis. It has been suggested that Parthenogenesis be merged into this article or section. ... For the religious belief, see Virgin Birth of Jesus. ... In botany, apomixis is asexual reproduction, without fertilization. ...


Apomixis and nucellar embryony

Main article: Apomixis
Main article: Nucellar embryony

Apomixis in plants is the formation of a new sporophyte without fertilization. It is important in ferns and in flowering plants, but is very rare in other seed plants. In flowering plants, the term "apomixis" is now most often used for agamospermy, the 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 embryony, the embryo is formed from the diploid nucellus tissue surrounding the embryo sac. Nucellar embryony occurs in some citrus seeds. Male apomixis can occur in rare cases, such as the Saharan Cypress where the genetic material of the embryo are derived entirely from pollen. The term "apomixis" is also used for asexual reproduction in some animals, notably water-fleas, Daphnia. In botany, apomixis is asexual reproduction, without fertilization. ... Most commercial citrus varieties produce mainly nucellar seedlings. ... Young sporophytes of the common moss Tortula muralis. ... Production of new individuals along a leaf margin of the air plant, Kalanchoë pinnata. ... Polyploid (in Greek: πολλαπλόν - multiple) cells or organisms contain more than one copy (ploidy) of their chromosomes. ... For other uses, see Dandelion (disambiguation). ... Most commercial citrus varieties produce mainly nucellar seedlings. ... Location of ovules inside a Helleborus foetidus flower Ovule literally means small egg. ... For other uses, see Citrus (disambiguation). ... Species Subgenus Daphnia Subgenus Hyalodaphnia D. galeata Subgenus Ctenodaphnia Daphnia are small, mostly planktonic, crustaceans, between 0. ...


Alternation between sexual and asexual reproduction

Some species alternate between the sexual and asexual strategies, an ability known as heterogamy, depending on conditions. 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. Many protists and fungi alternate between sexual and asexual reproduction. For example, the slime mold Dictyostelium undergoes binary fission as single-celled amboebae under favorable conditions. However, when conditions turn unfavorable, the cells aggregate and switch to sexual reproduction leading to the formation of spores. The hyphae of the common mold (Rhizopus) are capable of producing both mitotic as well as meiotic spores. Many algae similarly switch between sexual and asexual reproduction. Asexual reproduction is far less complicated than sexual reproduction. In sexual reproduction one must find a mate. Species Subgenus Daphnia Subgenus Hyalodaphnia D. galeata Subgenus Ctenodaphnia Daphnia are small, mostly planktonic, crustaceans, between 0. ... Sexual reproduction is a union that results in increasing genetic diversity of the offspring. ... Families & Genera Dictyosteliidae     Dictyostelium     Polysphondylium     Coenonia Actyosteliidae     Acytostelium The dictyostelids are a group of cellular slime moulds. ... Species Rhizopus nigricans Rhizopus stolonifer Rhizopus arrhizus Rhizopus azygosporus Rhizopus microsporus Rhizopus oligosporus Rhizopus oryzae Rhizopus schipperae and others Schematic diagram of Rhizopus is a genus of molds. ...


Examples in animals

A number of invertebrates and some less advanced vertebrates are known to alternate between sexual and asexual reproduction, or be exclusively asexual. Alternation is observed in a few types of insects, such as aphids (which will, under favourable conditions, produce eggs that have not gone through meiosis, essentially cloning themselves) and the cape bee Apis mellifera capensis (which can reproduce asexually through a process called thelytoky). A few species of amphibians and reptiles have the same ability (see parthenogenesis for concrete examples). A very unusual case among more advanced vertebrates is the female turkey's ability to produce fertile eggs in the absence of a male. The eggs result in often sickly, and nearly always male turkeys. This behaviour can interfere with the incubation of eggs in turkey farming.[3] Another unusual case would be certain species of sharks. [4] Families Adelgidae Aphididae Pemphigidae Phylloxeridae and several more Aphids (superfamily Aphidoidea) are small plant-sucking insects. ... Trinomial name Apis mellifera capensis Eschscholtz, 1822 Apis mellifera capensis, the Cape honeybee is a sub-species of the Western honeybee. ... The asexual production of female workers or queens by laying worker bees Category: ‪Beekeeping‬ ... For the religious belief, see Virgin Birth of Jesus. ... This article is about the domesticated animal raised for food. ...


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.[5] Classes Seisonoidea Bdelloidea Monogononta The rotifers make up a phylum of microscopic, pseudocoelomate animals. ... Matthew S. Meselson in 1964 Matthew Stanley Meselson (b. ...


Notes and references

  1. ^ Narra HP, Ochman H (2006). "Of what use is sex to bacteria?". Current Biology 16: R705-710. PMID 16950097. 
  2. ^ Teresa Pawlowska and John Taylor, "Organization of genetic variation in individuals of arbuscular mycorrhizal fungi", Nature, 2004, volume 427 (6976), pages 733-737.
  3. ^ Savage, Thomas F. (September 12, 2005). A Guide to the Recognition of Parthenogenesis in Incubated Turkey Eggs. Oregon State University. Retrieved on 2006-10-11.
  4. ^ Savage, Juliet Eilperin (May 23, 2007). Female Sharks Can Reproduce Alone, Researchers Find. Washington Post. Retrieved on 2008-04-27.
  5. ^ Pouchkina-Stantcheva, N.N., McGee, B.M. et al. (2007) Functional Divergence of Former Alleles in an Ancient Asexual Invertebrate. Science 318: 268-271

Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 284th day of the year (285th in leap years) in the Gregorian calendar. ... 2008 (MMVIII) is the current year, a leap year that started on Tuesday of the Anno Domini (or common era), in accordance with the Gregorian calendar. ... is the 117th day of the year (118th in leap years) in the Gregorian calendar. ...

Further reading

  • Graham, L., J. Graham, & L. Wilcox. 2003. Plant Biology. Pearson Education, Inc., Upper Saddle River, N.J.: pp. 258-259.
  • Raven, P.H., Evert, R.F., Eichhorn, S.E. 2005. Biology of Plants, 7th Edition. W.H. Freeman and Company Publishers, NY.

See also

Alternation of generations is a term usually applied to the reproductive cycle of ferns and fern allies, although it is more correct to say alternation of phases of a single generation (see Sporic meiosis lifecycle). ... Bacterial conjugation is the transfer of genetic material between bacteria through direct cell-to-cell contact. ... Biological reproduction is the biological process by which new individual organisms are produced. ... For the cloning of human beings, see human cloning. ... For the religious belief, see Virgin Birth of Jesus. ... For other uses, see Reproduction (disambiguation) Reproduction is the biological process by which new individual organisms are produced. ... This article or section does not cite its references or sources. ...

External links

  • Asexual reproduction
  • Intestinal Protozoa

 
 

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