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parthenogenesis

parthenogenesis

The Oxford Companion to the Body | 2001 | | Copyright

parthenogenesis is a type of asexual reproduction in which the offspring develops from unfertilized eggs. It is particularly common amongst arthropods and rotifers, can also be found in some species of fish, amphibians, birds, and reptiles, but not in mammals. Parthenogenetic development also occurs in some plants species, such as roses and orange trees.

Most animal species that reproduce parthenogenetically also display a phase of sexual behaviour and sexual reproduction. In most cases, parthenogenetic reproduction occurs when environmental conditions are favourable and there is plenty of food that can sustain the generation of large numbers of individuals in a short period of time. When external conditions change and food supplies become less abundant, or when the environment becomes unpredictable, these species shift to a sexual mode of reproduction. Although sexual reproduction is considerably slower and generates fewer organisms, it gives rise to individuals containing variations in their genetic material. Some of these individuals might be at an advantage over their predecessors, because they might be more able to adapt to new conditions.

In some species of insects, such as the aphids, parthenogenetic reproduction occurs in the spring and summer, when conditions are favourable for rapid population growth. As time goes by and conditions become less favourable, the parthenogenetically born individuals mate and lay fertilized eggs. These eggs hatch the following spring, when conditions are again favourable for another cycle of parthenogenetic reproduction.

In some species of ants, bees, and wasps, the ability to reproduce both sexually and asexually is part of the mechanism establishing sexual differences. Usually, females develop from unfertilized eggs, containing only half of the genetic material of the mother, whereas males develop from fertilized eggs, containing the genetic contributions of both mother and father.

In other species of insects, such as the rotifers, females produce unfertilized eggs that develop into females during the spring and summer. This process goes on for several generations. During the autumn, smaller eggs are laid, which develop into individuals lacking a digestive system, but capable of secreting sperm. These individuals mate with females, who then produce highly resistant, fertilized eggs that remain viable during long periods of unfavourable conditions. These eggs hatch in the following spring, giving rise only to females, who then engage in a new period of parthenogenetic reproduction.

Silvia Frenk
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COLIN BLAKEMORE and SHELIA JENNETT. "parthenogenesis." The Oxford Companion to the Body. 2001. Encyclopedia.com. 27 May. 2012 <http://www.encyclopedia.com>.

COLIN BLAKEMORE and SHELIA JENNETT. "parthenogenesis." The Oxford Companion to the Body. 2001. Encyclopedia.com. (May 27, 2012). http://www.encyclopedia.com/doc/1O128-parthenogenesis.html

COLIN BLAKEMORE and SHELIA JENNETT. "parthenogenesis." The Oxford Companion to the Body. 2001. Retrieved May 27, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O128-parthenogenesis.html

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parthenogenesis

The Columbia Encyclopedia, 6th ed. | 2011 | Copyright

parthenogenesis [Gr.,=virgin birth], in biology, a form of reproduction in which the ovum develops into a new individual without fertilization. Natural parthenogenesis has been observed in many lower animals (it is characteristic of the rotifers), especially insects, e.g., the aphid . In many social insects, such as the honeybee and the ant, the unfertilized eggs give rise to the male drones and the fertilized eggs to the female workers and queens. Parthenogenesis has also been observed in some snakes, fish, and monitor lizards. The phenomenon is rarer among plants (where it is called parthenocarpy) than among animals. Unusual patterns of heredity can occur in parthenogenetic organisms. For example, offspring produced by some types are identical in all inherited respects to the mother.

The phenomenon of parthenogenesis was discovered in the 18th cent. by Charles Bonnet . In 1900, Jacques Loeb accomplished the first clear case of artificial parthenogenesis when he pricked unfertilized frog eggs with a needle and found that in some cases normal embryonic development ensued. Artificial parthenogenesis has since been achieved in almost all major groups of animals, although it usually results in incomplete and abnormal development. Numerous mechanical and chemical agents have been used to stimulate unfertilized eggs. In 1936, Gregory Pincus induced parthenogenesis in mammalian (rabbit) eggs by temperature change and chemical agents. No successful experiments with human parthenogenesis have been reported.

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parthenogenesis

A Dictionary of Ecology | 2004 | | Copyright

parthenogenesis The development of an individual from an egg without that egg undergoing fertilization. It occurs in some groups of animals (e.g. flatworms, leeches, aphids, rotifers), in which males may be absent, and in some plants (e.g. dandelion). The eggs (ova) that develop in this way are usually diploid, so all offspring are genetically identical with the parent. Commonly, parthenogenesis with only females in the population alternates with ordinary sexual reproduction, which allows the recombination of genetic material and presents a need for males. This alternation is called heterogamy.
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MICHAEL ALLABY. "parthenogenesis." A Dictionary of Ecology. 2004. Encyclopedia.com. 27 May. 2012 <http://www.encyclopedia.com>.

MICHAEL ALLABY. "parthenogenesis." A Dictionary of Ecology. 2004. Encyclopedia.com. (May 27, 2012). http://www.encyclopedia.com/doc/1O14-parthenogenesis.html

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parthenogenesis

A Dictionary of Zoology | 1999 | | Copyright

parthenogenesis The development of an individual from an egg without that egg undergoing fertilization. It occurs in some groups of animals (e.g. flatworms, leeches, aphids, rotifers), in which males may be absent. The eggs (ova) that develop in this way are usually diploid, so all offspring are genetically identical with the parent. Commonly, parthenogenesis with only females in the population alternates with ordinary sexual reproduction, which allows the recombination of genetic material and presents a need for males. This alternation is called heterogamy.
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parthenogenesis

A Dictionary of Biology | 2004 | Copyright

parthenogenesis The development of an organism from an unfertilized egg. This occurs sporadically in many plants (e.g. dandelions and hawkweeds) and in a few animals, but in some species it is the main and sometimes only method of reproduction. For example, in some species of aphid, males are absent or very rare. The eggs formed by the females contain the full (diploid) number of chromosomes and are genetically identical. Variation is consequently very limited in species that reproduce parthenogenetically. See arrhenotoky; thelytoky.
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parthenogenesis

The Oxford Pocket Dictionary of Current English | 2009 | Copyright

par·the·no·gen·e·sis / ˌpär[unvoicedth]ənōˈjenəsis/ • n. Biol. reproduction from an ovum without fertilization, esp. as a normal process in some invertebrates and lower plants. DERIVATIVES: par·the·no·ge·net·ic / -jəˈnetik/ adj. par·the·no·ge·net·i·cal·ly / -jəˈnetik(ə)lē/ adv.

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parthenogenesis

World Encyclopedia | 2005 | Copyright

parthenogenesis Development of a female sex cell or gamete without fertilization. Since there is no involvement of a male gamete, it leads to the production of offspring that are genetically identical to the mother. This process occurs naturally among some plants and invertebrates, such as aphids.
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parthenogenesis

A Dictionary of Nursing | 2008 | Copyright

parthenogenesis (par-thin-oh-jen-i-sis) n. reproduction in which an organism develops from an unfertilized ovum. It is common in plants and occurs in some lower animals (e.g. aphids).
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parthenogenesis

A Dictionary of Plant Sciences | 1998 | | Copyright

parthenogenesis The development of an individual from an egg without fertilization; it occurs in some plants (e.g. dandelion).
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parthenogenesis

The Concise Oxford Dictionary of English Etymology | 1996 | | Copyright

parthenogenesis reproduction without sexual union. XIX. f. Gr. parthénos virgin + génesis birth, GENESIS.
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T. F. HOAD. "parthenogenesis." The Concise Oxford Dictionary of English Etymology. 1996. Encyclopedia.com. 27 May. 2012 <http://www.encyclopedia.com>.

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parthenogenesis

Oxford Dictionary of Rhymes | 2007 | Copyright

parthenogenesis •glacis, Onassis •abscess •anaphylaxis, axis, praxis, taxis •Chalcis • Jancis • synapsis • catharsis •Frances, Francis •thesis • Alexis • amanuensis •prolepsis, sepsis, syllepsis •basis, oasis, stasis •amniocentesis, anamnesis, ascesis, catechesis, exegesis, mimesis, prosthesis, psychokinesis, telekinesis •ellipsis, paralipsis •Lachesis •analysis, catalysis, dialysis, paralysis, psychoanalysis •electrolysis • nemesis •genesis, parthenogenesis, pathogenesis •diaeresis (US dieresis) • metathesis •parenthesis •photosynthesis, synthesis •hypothesis, prothesis •crisis, Isis •proboscis • synopsis •apotheosis, chlorosis, cirrhosis, diagnosis, halitosis, hypnosis, kenosis, meiosis, metempsychosis, misdiagnosis, mononucleosis, myxomatosis, necrosis, neurosis, osmosis, osteoporosis, prognosis, psittacosis, psychosis, sclerosis, symbiosis, thrombosis, toxoplasmosis, trichinosis, tuberculosis •archdiocese, diocese, elephantiasis, psoriasis •anabasis • apodosis •emphasis, underemphasis •anamorphosis, metamorphosis •periphrasis • entasis • protasis •hypostasis, iconostasis

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