Parthenogenesis



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The asexual, all-female whiptail species Cnemidophorus neomexicanus (center), which reproduces via parthenogenesis, is shown flanked by two sexual species having males, C. inornatus (left) and C. tigris (right), which hybridized naturally to form the C. neomexicanus species


Parthenogenesis (from the Greek παρθένος parthenos, "virgin", + γένεσις genesis, "creation") is an asexual form of reproduction found in females where growth and development of an embryo or seed occurs without fertilization by males.

Parthenogenesis occurs naturally in some species, including most lower plants, a Kalanchoe succulent plant genus of South Africa, invertebrates (e.g. water fleas, aphids, some bees, some scorpion species, and parasitic wasps), and vertebrates (e.g. some reptiles,[1] fish, and, very rarely, birds[2] and sharks[3]) and this type of reproduction has been induced artificially in other species.

The term is sometimes used inaccurately to describe reproduction modes in hermaphroditic species which can self-fertilize because they contain reproductive organs of both genders.

There also are numerous traditions of parthenogenesis in human cultures around the world, dating to the earliest of written records. Some of them relate to animals without sexual dimorphism, who were seen in contrast to animals with the trait. From their earliest writings, for instance, among the ancient Egyptians their observations of animals such as fish, snakes, white vultures, and others without the trait led them to presume that all members of those species were female and reproduced through parthenogenesis. When those animal species became associated with human identities or deities in their cultures, the concept of parthenogenesis was transferred also.

Asexual reproduction

Parthenogenesis is a form of asexual reproduction in which females produce eggs that develop without fertilization. Parthenogenesis is seen to occur naturally in aphids, daphnia, rotifers, and some other invertebrates, as well as in many plants. Komodo dragons and sharks have recently been added to the list of vertebrates—along with several genera of fish, amphibians, and reptiles—that exhibit differing forms of asexual reproduction, including true parthenogenesis, gynogenesis, and hybridogenesis (an incomplete form of parthenogenesis).

The offspring of parthenogenesis will be all female if two like chromosomes determine the female gender (such as the XY sex-determination system), but male if two like chromosomes determine the male gender (such as the ZW sex-determination system), because the process involves the inheritance and subsequent duplication of only a single sex chromosome. The offspring may be capable of sexual reproduction, if this mode exists in the species. A parthenogenetic offspring is sometimes called a parthenogen. As with all types of asexual reproduction, there are both costs (low genetic diversity and susceptibility to adverse mutations that might occur) and benefits (reproduction without the need for a male) associated with parthenogenesis. Asexual reproduction existed alone from the beginning of life on Earth for many epochs, all life being female and reproducing via what are called mother and daughter cells or through parthenogenesis. When sexual reproduction arose (presumably through mutation) it introduced a means to expand genetic diversity through the partial contribution of the male, providing more options for the survival of the species in which it began. Many species followed this reproductive path successfully, some to the exclusion of the asexual pattern from which it arose, some enabling both, some retaining the capacity to revert to asexual reproduction—if necessary, and yet others that abandoned sexual reproduction and reverted to the asexual. There are species, such as some Kalanchoe plants, that once had the capacity to reproduce sexually, but wherein no males ever have been discovered and the species reproduces prolifically via its retained asexual methods alone.

Parthenogenesis is distinct from artificial animal cloning, a process where the new organism is identical to the cell donor. Parthenogenesis is truly a reproductive process which creates a new individual or individuals from the naturally varied genetic material contained in the eggs of the mother. A litter of animals resulting from parthenogenesis may contain all genetically unique siblings without any twins or multiple numbers from the same genetic material.

In animals with an XY chromosome system where parthenogenic offspring are female, parthenogenic offspring of a parthenogen are, however, all genetically identical to that daughter when she becomes a mother and her offspring will be identical to each other, as a parthenogen is homozygous. Each sibling of the first generation of parthenogens will, therefore, create a linage that carries only her unique genes when reproducing via parthenogenesis.

Parthenogenesis may be achieved through an artificial process, however, as described below under the discussion of mammals.

The alternation between parthenogenesis and sexual reproduction is called heterogamy. Forms of reproduction related to parthenogenesis, but that only require the presence of sperm that do not fertilize an egg, are known as gynogenesis and hybridogenesis.

Insects

An example of non-viable parthenogenesis is common among domesticated honey bees. The queen bee is the only fertile female in the hive; if she dies without the possibility for a viable replacement queen, it is not uncommon for the worker bees to lay eggs.

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Honey Bee on a plum blossom
Worker bees are unable to mate, and the unfertilized eggs produce only drones (males), which can only mate with a queen. Thus, in a relatively short period, all the worker bees die off, and the new drones follow.

In one subspecies from South Africa, Apis mellifera capensis, workers are capable of producing diploid eggs parthenogenetically, and thus the queen can be replaced if she dies.

It is believed that a few other bees may be truly parthenogenetic, for example, at least one species of small carpenter bee, in the genus Ceratina. Many parasitic wasps are known to be parthenogenetic, sometimes due to infections by Wolbachia.

In Cataglyphis cursor, a European formicine ant, the queen can reproduce by parthenogenesis. The workers are fertile and can mate with the males.[4]

In little fire ants, Wasmannia auropunctata, queens produce more queens through parthenogenesis. Usually, eggs fertilized by the males will develop into sterile workers. In some eggs, males cause the female genetic material to be ablated from the zygote, in a process called ameiotic parthenogenesis. In this way, males can pass on their genes by cloning themselves. This is the first example of an animal species where both females and males can clone themselves.[5]

Reptiles

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Komodo Dragon, Varanus komodoensis, is confirmed to be able to reproduce naturally by parthenogenesis
Most reptiles reproduce sexually, but parthenogenesis has been observed to occur naturally in certain species of whiptails, geckos, rock lizards[1], and Komodo dragons.

Parthenogenesis has been studied extensively in the New Mexico whiptail (genus Cnemidophorus), of which 15 species reproduce exclusively by parthenogenesis. These lizards live in the dry and sometimes harsh climate of the southwestern United States and northern Mexico. All these asexual species appear to have arisen through the hybridization of two or three of the sexual species in the genus leading to polyploid individuals. The mechanism by which the mixing of chromosomes from two or three species can lead to parthenogenetic reproduction is unknown. Because multiple hybridization events can occur, individual parthenogenetic whiptail species can consist of multiple independent asexual lineages. Within lineages, there is very little genetic diversity, but different lineages may have quite different genotypes.

An interesting aspect to reproduction in these asexual lizards is that mating behaviours are still seen, although the populations are all female. One female plays the role played by the male in closely related species, and mounts the female that is about to lay eggs. This behaviour is due to the hormonal cycles of the females, which cause them to behave like males shortly after laying eggs, when levels of progesterone are high, and to take the female role in mating before laying eggs, when estrogen dominates. Lizards who act out the courtship ritual have greater fecundity than those kept in isolation, due to the increase in hormones that accompanies the mounting. So, although the populations lack males, they still require sexual behavioral stimuli for maximum reproductive success.

Recently, the Komodo dragon, which normally reproduces sexually, was found also to be able to reproduce asexually by parthenogenesis.[6][7] Because the genetics of sex determination in Komodo Dragons uses the WZ system (where WZ is female, ZZ is male, and WW is inviable) the offspring of this process will be ZZ (male) or WW (inviable), with no WZ females being born. A case has been documented of a Komodo Dragon switching back to sexual reproduction after a known parthenogenetic event. [8] It has been postulated that this gives an advantage to colonisation of islands, where a single female could theoretically have male offspring asexually, then switch to sexual reproduction with them to maintain higher level of genetic diversity than asexual reproduction alone can generate.[8]

Parthenogenesis may also occur naturally when males and females are both present, explaining why the wild Komodo dragon population is approximately 75 percent male.

Sharks

[9] [10] [11] [12] [13] [14]

In 2001 a bonnethead, a type of small hammerhead shark, was thought to have produced a pup, born live on the 14th December 2001 at Henry Doorly Zoo in Nebraska, in a tank containing three female hammerheads, but no males. The pup was thought to have been conceived through parthenogenic means. The shark pup was apparently killed by a stingray within three days of birth.[15] The investigation of the birth was conducted by the research team from Queen's University Belfast, the Southeastern University in Florida, and Henry Doorly Zoo itself, and concluded after DNA testing that the reproduction was parthenogenic. The testing showed the female pup's DNA matched only one female who lived in the tank, and that no male DNA was present in the pup. The pup was not a twin or clone of her mother, but rather, contained only half of her mother's DNA ("automictic parthenogenesis"). This type of reproduction had been seen before in bony fish, but never in cartilaginous fish such as sharks, until this documentation.

In 2002, two white-spotted bamboo sharks were born at the Belle Isle Aquarium in Detroit. They hatched 15 weeks after laying. The birth baffled experts as the mother shared an aquarium with only one other female shark. The female bamboo sharks had laid eggs in the past. This is not unexpected, as many animals will lay infertile eggs even if there is not a male to fertilize them. Normally, the eggs are assumed to be infertile and are discarded. This batch of eggs was left undisturbed by the curator as he had heard about the previous birth in 2001 in Nebraska and wanted to observe whether they would hatch.

Other possibilities had been considered for the birth of the Detroit bamboo sharks including thoughts that the sharks had been fertilized by a male and stored the sperm for a period of time as well as the possibility that the Belle Isle bamboo shark is a hermaphrodite, harboring both male and female sex organs, and capable of fertilizing its own eggs, but that is not confirmed.

The repercussions of parthenogenesis in sharks, which fails to increase the genetic diversity of the offspring, is a matter of concern for shark experts, taking into consideration conservation management strategies for this species, particularly in areas where there may be a shortage of males due to fishing or environmental pressures.

Unlike Komodo dragons, which have a WZ chromosome system and produce even male (ZZ) offspring by parthenogenesis, sharks have an XY chromosome system, so they produce only female (XX) offspring by parthenogenesis. As a result, sharks cannot restore a depleted male population through parthenogenesis, so an all-female population must come in contact with an outside male before sexual reproduction resulting in males can occur.

Mammals

There are no known cases of mammalian parthenogenesis in the wild.

In April 2004, scientists at Tokyo University of Agriculture used parthenogenesis successfully to create a fatherless mouse.

In theory, artificial human parthenogenesis could be used to reproduce humans, but this is highly unlikely due to ethical concerns. Use of an electrical or chemical stimulus can produce the beginning of the process of parthenogenesis in the asexual development of viable offspring.

Parthenogenesis in mice and monkeys often results in abnormal development. This is because mammals have imprinted genetic regions, where either the maternal or the paternal chromosome is inactivated in the offspring in order for development to proceed normally. A mammal created by parthenogenesis would thus have double doses of maternally imprinted genes and lack paternally imprinted genes, leading to developmental abnormalities if present in the genes of the mother. As a consequence, research on human parthenogenesis is focused on the production of embryonic stem cells for use in medical treatment, not as a reproductive strategy.

On August 2, 2007, after much independent investigation, it was revealed that discredited South Korean scientist, Hwang Woo-Suk, produced the first human embryos through parthenogenesis. Initially, Hwang claimed he and his team had extracted stem cells from cloned human embryos, a result which was later found to be fabricated. Further examination of the chromosomes of these cells show the same indicators of parthenogenesis in those extracted stem cells, as are found in the mice created by Tokyo scientists in 2004. Although Hwang deceived the world about being the first to create artificially cloned human embryos, he did contribute a major breakthrough to stem cell research by creating human embryos using parthenogenesis. The process may offer a way for creating stem cells that are genetically matched to a particular woman for the treatment of degenerative diseases. [16]

The news of Hwang's breakthrough came just a month after an announcement from the International Stem Cell Corporation (ISC), a California based stem cell research company, that they had successfully created the first human embryos through parthenogenesis. Although the truth about the results of Hwang's work were just discovered, those embryos were created by him and his team before February 2004, making Hwang the first to perform the human process of parthenogenesis successfully. In 2006, a group of Italian researchers announced they had achieved the same feat, but have yet to publish their results, which eventually, if confirmed, may make ISC only the third organization to achieve artificial parthenogenesis of humans in the laboratory. [17]

Gynogenesis

A form of asexual reproduction related to parthenogenesis is gynogenesis. Here offspring are produced by the same mechanism as in parthenogenesis, but with the requirement that the egg be stimulated by the presence of sperm in order to develop. However, the sperm cell does not contribute any genetic material to the offspring. Since gynogenetic species are all female, activation of their eggs requires mating with males of a closely related species for the stimulus needed. Some salamanders of the genus Ambystoma are gynogenetic and appear to have been so for over a million years. It is believed that the success of those salamanders may be due to a rare fertilization of eggs by a male, introducing new material to the gene pool, which may result from perhaps, only one mating out of a million.

Hybridogenesis

In hybridogenesis reproduction is not completely asexual, but instead hemiclonal: half the genome passes intact to the next generation, while the other half is discarded.

Hybridogenetic females can mate with males of a "donor" species and both will contribute genetic material to the offspring. When the female offspring produce their own eggs, however, the eggs will contain no genetic material from their father, only the chromosomes from the offspring's own mother; the set of genes from the father is invariably discarded. This process continues, so that each generation is half (or hemi-) clonal on the mother's side and half new genetic material from the father's side. This form of reproduction is seen in some live-bearing fish of the genus Poeciliopsis as well as in the waterfrog Rana esculenta and the donor waterfrog species Rana lessonae.

A graphical representation of this can be seen through this link.

Automictic parthenogenesis

This is defined as a reproduction resulting when the set of chromosomes acquired from the mother, pairs with an exact copy of itself, which can be described as "half a clone".[18] The animal still is unique and not a clone of her mother. In typical parthenogenesis the individual offspring differ from one another and their mother.

See also

Notes

1. ^ Halliday, Tim R.; Kraig Adler (eds.) (1986). Reptiles & Amphibians. Torstar Books, p. 101. ISBN 0-920269-81-8. 
2. ^ 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.
3. ^ "Female Sharks Can Reproduce Alone, Researchers Find", Washington Post, Wednesday, May 23, 2007; Page A02
4. ^ "Conditional Use of Sex and Parthenogenesis for Worker and Queen Production in Ants" Pearcy M, et al. Science 306:1780, 2004.
5. ^ "Clonal reproduction by males and females in the little fire ant" Fournier D, et al. Nature 435:1230, 2005.
6. ^ "No sex please, we're lizards", Roger Highfield, Daily Telegraph, 21 December 2006
7. ^ "Parthenogenesis in Komodo dragons"Watts PC, et al. . Nature 444, p1021, 2006.
8. ^ Virgin birth of dragons, The Hindu, 25 January 2007, Retrieved 3 February 2007
9. ^ Female sharks capable of virgin birth, Shawn Pogatchnik, Associate Press, MSNBC, 22 May 2007
10. ^ Captive shark had 'virgin birth', BBC News, 23 May 2007
11. ^ Shark Gives "Virgin Birth" in Detroit, Hillary Mayell, National Geographic News, 26 September 2002
12. ^ Virgin Shark Gives Birth, LiveScience, 22 May 2007
13. ^ Reproduction in a Bamboo Shark Unexplained, Veterinary & Aquatic Services Department, Drs. Foster & Smith, Inc. October 2002
14. ^ Female Shark Reproduced Without Male DNA, Scientists Say
15. ^ [1]
16. ^ [2]
17. ^ [3]
18. ^ Milius, S. (2007) Virgin Birth: Shark has daughter without a dad, Science News vol 171, pp 323-324. (references)
19. ^ Hore, T.A. et al., Construction and evolution of imprinted loci in mammals, Trends Genet. (2007), doi:10.1016/j.tig.2007.07.003

Further reading

  • Dawley, Robert M. & Bogart, James P. (1989). Evolution and Ecology of Unisexual Vertebrates. Albany, New York: New York State Museum. ISBN 1-55557-179-4.
  • Futuyma, Douglas J. & Slatkin, Montgomery. (1983). Coevolution. Sunderland, Mass: Sinauer Associates. ISBN 0-87893-228-3.
  • Maynard Smith, John. (1978). The Evolution of Sex. Cambridge: Cambridge University Press. ISBN 0-521-29302-2.
  • Michod, Richard E. & Levin, Bruce R. (1988). The Evolution of Sex. Sunderland, Mass: Sinauer Associates. ISBN 0-87893-459-6.
  • Schlupp, I. (2005) The evolutionary ecology of gynogenesis. Annu. Rev. Ecol. Evol. Syst. 36: 399-417.
  • Simon, Jean-Christophe, Rispe, Claude & Sunnucks, Paul. (2002). Ecology and evolution of sex in aphids. Trends in Ecology & Evolution, 17, 34-39.
  • Stearns, Stephan C. (1988). The Evolution of Sex and Its Consequences (Experientia Supplementum, Vol. 55). Boston: Birkhauser. ISBN 0-8176-1807-4.
  • Phillip C. Watts, Kevin R. Buley, Stephanie Sanderson, Wayne Boardman, Claudio Ciofi and Richard Gibson. (2006). Parthenogenesis in Komodo dragons. Nature 444, 1021-1022

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For other meanings of seed, see seed (disambiguation).


SEED

General
KISA
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SEED
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Fertilization (also known as conception, fecundation and syngamy), is fusion of gametes to form a new organism of the same species. In animals, the process involves a sperm fusing with an ovum, which eventually leads to the development of an embryo.
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Male (♂) refers to the sex of an organism, or part of an organism, which produces small mobile gametes, called spermatozoa. Each spermatozoon can fuse with a larger female gamete or ovum, in the process of fertilisation.
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Plantae
Haeckel, 1866[1]

Divisions

Green algae
  • Chlorophyta
  • Charophyta
Land plants (embryophytes)
  • Non-vascular land plants (bryophytes)

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Kalanchoe
Adans.

Species

Around 125, see text.
Synonyms

Bryophyllum

Kalanchoe is a genus of about 125 species of tropical, succulent flowering plants in the Family Crassulaceae, mainly native to the Old World
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Invertebrate is an English word that describes any animal without a spinal column. The group includes 97% of all animal species — all animals except those in the Chordate subphylum Vertebrata (fish, reptiles, amphibians, birds and mammals).
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Water flea is a generic term for a number of small aquatic crustacea characterised by their jumping or jerky mode of swimming. Most are between 0.1 mm and 3 mm in length. Most commonly, they will be species of Daphnia
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Aphidoidea

Families

There are 10 families:
  • Anoeciidae
  • Aphididae
  • Drepanosiphidae
  • Greenideidae
  • Hormaphididae
  • Lachnidae
  • Mindaridae
  • Pemphigidae
  • Phloeomyzidae
  • Thelaxidae


Aphids, also known as
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BEE may refer to:
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  • Biblical Education by Extension, a Christian program designed to instruct theology in countries with weak theological infrastructure.

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Scorpiones
C. L. Koch, 1837

Superfamilies

Pseudochactoidea
Buthoidea
Chaeriloidea
Chactoidea
Iuroidea
Scorpionoidea
See classification for families.
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parasitic wasp refers to a large, artificial assemblage of Hymenopteran superfamilies which are primarily parasitoids of other animals, mostly other arthropods. Many of them, such as the family Braconidae, are considered beneficial because they control populations of agricultural
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Vertebrata
Cuvier, 1812

Classes and Clades

See below
Vertebrates are members of the subphylum Vertebrata (within the phylum Chordata), specifically, those chordates with backbones or spinal columns.
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Sauropsida*
Goodrich, 1916

Subclasses
  • Anapsida
  • Diapsida
Synonyms
  • Reptilia Laurenti, 1768
Reptiles are tetrapods and amniotes, animals whose embryos are surrounded by an amniotic membrane, and members of the class
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Aves
Linnaeus, 1758

Orders

About two dozen - see section below

Birds (class Aves) are bipedal, warm-blooded, egg-laying vertebrate animals.
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SHARK

General
Vincent Rijmen, Joan Daemen, Bart Preneel, Antoon Bosselaers, Erik De Win
1996

KHAZAD, Rijndael

Cipher detail
Key size(s):| 128 bits

Block size(s):| 64 bits
Substitution-permutation network
6

In cryptography,
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hermaphrodite is an organism that posses both male and female genetalia.[1] In many species, hermaphroditism is a common part of the life-cycle, particularly in some asexual animals and some plants.
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Sexual dimorphism is the systematic difference in form between individuals of different sex in the same species. Examples include size, color, and the presence or absence of parts of the body used in courtship displays or fights, such as ornamental feathers, horns, antlers or tusks.
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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.
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Aphidoidea

Families

There are 10 families:
  • Anoeciidae
  • Aphididae
  • Drepanosiphidae
  • Greenideidae
  • Hormaphididae
  • Lachnidae
  • Mindaridae
  • Pemphigidae
  • Phloeomyzidae
  • Thelaxidae


Aphids, also known as
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Daphnia
Müller, 1785

Species
  • Subgenus Daphnia
:D. ambigua
:D. arenata
:D. catawba
:D. cheraphila
:D.

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Rotifera
Cuvier, 1798

Classes
Monogononta
Digononta
The rotifers make up a phylum of microscopic and near-microscopic pseudocoelomate animals. They were first described by John Harris in 1696 (Hudson and Gosse, 1886).
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V. komodoensis

Binomial name
Varanus komodoensis
Ouwens, 1912

Komodo dragon distribution


The Komodo Dragon (Varanus komodoensis
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The XY sex-determination system is the sex-determination system found in humans, most other mammals, some insects (Drosophila) and some plants (Ginkgo). In the XY sex-determination system, females have two of the same kind of sex chromosome (XX), and are called
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The ZW sex-determination system is a system that birds, some fishes, and some insects (including butterflies and moths) use to determine the sex of their offspring. The ovum determines the sex of the offspring in this system, in contrast to the XY sex-determination system and the
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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.
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Dolly (July 5, 1996 – February 14, 2003), a ewe, was the first mammal to be cloned from an adult somatic cell. The cell used was a mammary cell, which is why she was named Dolly, after the curvaceous country western singer Dolly Parton.
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