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A '''clone''' is any [[cell]] or individual which is identical to another.
{{Short description|Process of producing genetically-identical copies}}
'''Cloning''' refers to the process of creating genetically identical copies of biological entities. A '''clone''' is any cell or individual that is genetically identical to another. Cloning can occur naturally or be artificially induced in a laboratory setting.
In biology, '''cloning''' is the process of producing one or more [[genetic]]ally-identical individuals. With whole individuals, it usually means the deliberate production of an identical copy. This was first achieved in [[mammal]]s with the famous [[Dolly (sheep)|Dolly the sheep]]. [[Human]] [[identical twins]] are ''natural clones''. So are the offspring of [[asexual reproduction]], and any [[parthenogenesis|parthenogenetic]] reproduction which does not involve [[meiosis]].<ref>If there is [[crossing over]] between the paired [[chromosome]]s in the cells leading up to the egg, then the eggs will not be identical.</ref>
== Natural Cloning ==
Cloning is a common process in nature, particularly among organisms that reproduce asexually.
Cloning is natural to some animals, but rare in [[mammals]]. An exception is the [[Nine-banded armadillo]], which normally gives birth to identical [[Twin|quadruplet]]s.
=== Identical Twins ===
In [[humans]] and other [[mammals]], natural cloning occurs when a fertilized [[zygote]] splits, producing [[identical twins]]. These individuals have the same [[genome]] and are considered natural clones.
In [[genetics]] and [[cell biology]], cloning refers especially to the [[DNA]] sequence, and by implication all the other [[macromolecule]]s.
=== Asexual Reproduction ===
Many [[bacteria]], [[protists]], and some [[plants]] and [[invertebrates]] reproduce asexually, producing clones of themselves. Examples include binary fission in bacteria and vegetative propagation in plants.
Clones in cell lines occur, but there are some obvious provisos. Changes to the DNA in any shape or form means the daughter cells are not identical with the mother cells. Typically during development genes are switched on and off, and the daughter cells gradually become differentiated into mature tissue cells. These are not identical with the original [[stem cell]]s, so they are clones only in the sense of being ''derived'' from the same mother cell.
=== Parthenogenesis ===
[[Parthenogenesis]] is a form of asexual reproduction in which an [[ovum]] develops into an individual without fertilization. It occurs in some [[insects]], [[reptiles]], and rare cases in vertebrates. Since [[meiosis]] is often absent or altered, the offspring are genetically similar to the parent, constituting clones.
The [[laboratory]] copying of a molecule to produce exact copies is also called cloning.
=== Notable Example in Mammals ===
Although rare in mammals, the [[Nine-banded armadillo]] typically gives birth to genetically identical quadruplets, providing a natural example of mammalian cloning.
== Not quite so identical ==
== Artificial Cloning ==
Although clones start off identical, they may not stay that way. [[Identical twin]]s always have slightly different [[phenotype]]s.<ref>{{Cite journal|last=Machin |first=G.A. 1996. Some causes of genotypic and phenotypic discordance in monozygotic twin pairs |journal=American Journal of Medical Genetics |volume=61 |issue=3 |pages=216–228 |pmid=8741866 |doi=10.1002/(SICI)1096-8628(19960122)61:3<216::AID-AJMG5>3.0.CO;2-S |url= |accessdate=}}</ref><ref>{{cite journal|author=Schmid 2000. |pmid=11113914 | volume=20 | issue=12 | title=Prenatal diagnosis of heterokaryotypic mosaic twins discordant for fetal sex. | journal=Prenat Diagn | pages=999–1003}}</ref>
In [[biology]] and [[biotechnology]], cloning can refer to different techniques used to produce genetic duplicates.
Although monozygotic twins are genetically ''almost'' identical, a 2012 study of 92 pairs of monozygotic twins found that monozygotic twins acquire several hundred genetic differences early in [[foetus|foetal]] development. This is caused by [[mutation]]s (or copy errors) taking place in the DNA of each twin after the splitting of the embryo.<ref>{{cite web|url=http://www.dailymail.co.uk/sciencetech/article-2232148/Identical-twins-genetically-different-research-suggests.html |title=Identical twins are genetically different, research suggests | Mail Online |publisher=Dailymail.co.uk |date=2012-11-13 |accessdate=2013-09-16}}</ref> It is estimated that, on average, a set of monozygotic twins will have about 360 genetic differences that occurred early in foetal development. However, these changes may have little practical effect. In practice, identical twins look and act in a very similar way.
=== Reproductive Cloning ===
Reproductive cloning creates an entire organism genetically identical to another. The most famous example is '''[[Dolly the sheep]]''', the first cloned mammal created in 1996 using [[somatic cell nuclear transfer]] (SCNT). In this process, the nucleus of a somatic cell is transferred into an enucleated egg cell.
Another cause of difference between monozygotic twins is [[Epigenetics|epigenetic modification]]. These are caused by differing environmental influences throughout their lives, which affects which genes are switched on or off. A study of 80 pairs of monozygotic twins ranging in age from three to 74 showed that the youngest twins have relatively few [[epigenetic]] differences. The number of epigenetic differences increases with age. Fifty-year-old twins had over three times the epigenetic difference of three-year-old twins. Twins who had spent their lives apart (such as those adopted by two different sets of parents at birth) had the greatest difference.<ref>{{Cite journal|first=Fraga, Mario F; Ballestar, Esteban et al. |title=Epigenetic differences arise during the lifetime of monozygotic twins |journal=Proc. Natl. Acad. Sci. U.S.A. |volume=102 |issue=30 |pages=10604–9 |year=2005 |pmid=16009939 |pmc=1174919 |doi=10.1073/pnas.0500398102 }}</ref> However, certain characteristics become more alike as twins age, such as IQ and personality. This phenomenon illustrates the influence of genetics in many aspects of human characteristics and behaviour.<ref>{{Cite book|last=Segal |first=Nancy L. |title=Entwined lives: twins and what they tell us about human behavior |publisher=Dutton |location=New York |year=1999 |pages= |isbn=0-525-94465-6 |oclc= 40396458|doi= }}</ref><ref>{{Cite book|last=Plomin |first=Robert |title=Behavioral genetics |publisher=Worth Pubs |location=New York |year=2001 |pages= |isbn=0-7167-5159-3 |oclc=43894450}}</ref><ref>Mandler,G. (2001) Apart from genetics: What makes monozygotic twins similar? ''Journal of Mind and Behavior''. '''22''', 147-159.</ref>
=== Therapeutic Cloning ===
Therapeutic cloning involves producing [[embryonic stem cells]] for medical research or treatment. These cells can develop into any type of tissue and are genetically identical to the donor.
== Species cloned ==
=== Molecular Cloning ===
* [[Carp]]: (1963) In [[China]], embryologist [[Tong Dizhou]] produced the world's first cloned fish by inserting the DNA from a cell of a male carp into an egg from a female carp. He published the findings in a Chinese science journal.<ref>{{cite web |url=https://www.pbs.org/bloodlines/timeline/text_timeline.html |title=Bloodlines timeline |author= |work= |publisher=PBS.org|accessdate= }}</ref>
In [[genetics]] and [[cell biology]], cloning also refers to the process of copying [[DNA]] sequences. This includes:
* [[Mice]]: (1986) A mouse was the first mammal successfully cloned from an early embryonic cell. [[Soviet]] scientists Chaylakhyan, Veprencev, Sviridova, and Nikitin had the mouse "Masha" cloned. Research was published in the journal "Biofizika" volume ХХХII, issue 5 of 1987.<ref>{{cite web| title=Кто изобрел клонирование?| archiveurl=https://web.archive.org/web/20041223221951/http://www.whoiswho.ru/russian/Curnom/22003/cl.htm| archivedate=2004-12-23| url=http://www.whoiswho.ru/russian/Curnom/22003/cl.htm}} (in Russian)</ref>
* [[Sheep]]: (1996) From early embryonic cells by Steen Willadsen. Megan and Morag[19] cloned from differentiated embryonic cells in June 1995 and Dolly the sheep from a somatic cell in 1997.<ref>{{cite journal |author=McLaren A |title=Cloning: pathways to a pluripotent future |journal=Science |volume=288 |issue=5472 |pages=1775–80 |year=2000 |pmid=10877698 |doi=10.1126/science.288.5472.1775}}</ref>
* [[Monkey]]: (2000) Tetra, from embryo splitting.<ref>[[CNN]]: [http://archives.cnn.com/2000/NATURE/01/13/monkey.cloning/ Researchers clone monkey by splitting embryo] 2000. Retrieved 2008-08-05.</ref><ref>{{cite news|author=Dean Irvine |url=http://edition.cnn.com/2007/WORLD/europe/11/16/ww.humancloning/index.html?iref=allsearch |title=You, again: are we getting closer to cloning humans? - CNN.com |publisher=Edition.cnn.com |date=2007 |accessdate=2010-08-04}}</ref>
* [[Gaur]]: (2001) was the first endangered species cloned.<ref>{{cite news| url=http://archives.cnn.com/2001/NATURE/01/12/cloned.gaur/index.html | work=CNN | title=First cloned endangered species dies 2 days after birth | date= 2001 | accessdate=April 30, 2010}}</ref>
* [[Cattle]]: Alpha and Beta males 2001 and 2005, Brazil.<ref>Camacho, Keite. [http://www.radiobras.gov.br/materia_i_2004.php?materia=226261&q=1&editoria= Embrapa clona raça de boi ameaçada de extinção]. Agência Brasil. 2005 (in Portuguese) Retrieved 2008-08-05</ref>
* [[Cat]]: CopyCat "CC" (female, late 2001), Little Nicky, 2004, was the first cat cloned for commercial reasons.<ref>{{cite news|url=http://news.bbc.co.uk/1/hi/world/americas/4120179.stm |title=Americas | Pet kitten cloned for Christmas |publisher=BBC News |date=2004 |accessdate=2010-08-04}}</ref>
* [[Dog]]: (2005) Snuppy, a male Afghan hound was the first cloned dog.<ref>{{cite web|url=http://news.nationalgeographic.com/news/2005/08/photogalleries/dogclone/ |title=First dog clone |publisher=News.nationalgeographic.com |accessdate=2010-08-04}}</ref>
* [[Rat]]: (2003) Ralph, the first cloned rat.<ref>{{cite news| url=http://news.bbc.co.uk/2/hi/science/nature/3136776.stm | work=BBC News | title=Rat called Ralph is latest clone | date=September 25, 2003 | accessdate=April 30, 2010}}</ref>
* [[Mule]]: (2003) Idaho Gem, a john mule, was the first horse-family clone.<ref>{{cite news|author=Associated Press August 25, 2009 |url=http://www.latimes.com/news/nationworld/nation/la-me-gordon-woods25-2009aug25,0,5372986.story |title=Gordon Woods dies at 57; Veterinary scientist helped create first cloned mule |publisher=latimes.com |date=2009-08-25 |accessdate=2010-08-04}}</ref>
* [[Horse]]: (2003) Prometea, a [[Haflinger]] female, was the first horse clone.<ref>{{cite web|url=https://www.newscientist.com/article/dn4026-worlds-first-cloned-horse-is-born.html |title=World's first cloned horse is born - 06 August 2003 |publisher=New Scientist |accessdate=2010-08-04}}</ref>
* [[Water Buffalo]]: (2009) Samrupa was the first cloned water buffalo. It was born at India's Karnal National Diary Research Institute but died five days later of a lung infection.<ref>{{cite web|author=Kounteya Sinha, TNN, Feb 13, 2009, 12.33am IST |url=http://timesofindia.indiatimes.com/India-clones-worlds-first-buffalo/articleshow/4120044.cms |title=India clones world's first buffalo - India - The Times of India |publisher=Timesofindia.indiatimes.com |date=2009 |accessdate=2010-08-04}}</ref>
* [[Camel]]: (2009) The first cloned camel.<ref>{{cite news| url = https://www.telegraph.co.uk/news/newstopics/howaboutthat/5153780/Worlds-first-cloned-camel-unveiled-in-Dubai.html | title = World's first cloned camel unveiled in Dubai | first = Richard | last = Spencer | publisher = Telegraph.co.uk | date = 2009 | accessdate = April 15, 2009 | location=London}}</ref>
== References ==
* [[Gene cloning]] – copying specific DNA sequences for research or biotechnology.
{{Reflist}}
* [[Plasmid]] cloning – inserting DNA into bacterial plasmids for propagation.
* [[Polymerase chain reaction]] (PCR) – amplifying DNA segments in vitro.
== Cloning in Cell Biology ==
Cell lines in research are often derived from a single cell, making them clonal. However, during [[cell division]], mutations and gene expression changes can lead to cellular differentiation. Although the cells originate from a common ancestor, they are not always genetically or functionally identical.
=== Stem Cells ===
[[Stem cells]] are undifferentiated cells capable of giving rise to various cell types. While daughter cells may be derived from the same stem cell, they become distinct as they specialize into tissue-specific cells.
== Applications of Cloning ==
Cloning has numerous applications in modern science, medicine, and agriculture:
* Creating genetically identical animals for research
* Preserving endangered species
* Producing genetically modified organisms (GMOs)
* Developing regenerative therapies using stem cells
* Mass-producing proteins and pharmaceuticals
== Ethical Considerations ==
Cloning, especially reproductive cloning in humans, raises ethical concerns including identity, individuality, and the potential for misuse. These issues are widely debated in the fields of bioethics, law, and public policy.
== See also ==
* [[Asexual reproduction]]
* [[Somatic cell nuclear transfer]]
* [[Genetic engineering]]
* [[Dolly the sheep]]
* [[Stem cell]]
* [[Parthenogenesis]]
* [[Gene cloning]]
{{stub}}
[[Category:Genetics]]
[[Category:Genetics]]
[[Category:Biotechnology]]
[[Category:Cell biology]]
[[Category:Cell biology]]
[[Category:Developmental biology]]
[[Category:Cloning]]
[[Category:Biological reproduction]]
[[Category:Reproduction]]
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Latest revision as of 04:00, 30 March 2025
Process of producing genetically-identical copies
Cloning refers to the process of creating genetically identical copies of biological entities. A clone is any cell or individual that is genetically identical to another. Cloning can occur naturally or be artificially induced in a laboratory setting.
In humans and other mammals, natural cloning occurs when a fertilized zygote splits, producing identical twins. These individuals have the same genome and are considered natural clones.
Many bacteria, protists, and some plants and invertebrates reproduce asexually, producing clones of themselves. Examples include binary fission in bacteria and vegetative propagation in plants.
Parthenogenesis is a form of asexual reproduction in which an ovum develops into an individual without fertilization. It occurs in some insects, reptiles, and rare cases in vertebrates. Since meiosis is often absent or altered, the offspring are genetically similar to the parent, constituting clones.
Although rare in mammals, the Nine-banded armadillo typically gives birth to genetically identical quadruplets, providing a natural example of mammalian cloning.
Reproductive cloning creates an entire organism genetically identical to another. The most famous example is Dolly the sheep, the first cloned mammal created in 1996 using somatic cell nuclear transfer (SCNT). In this process, the nucleus of a somatic cell is transferred into an enucleated egg cell.
Therapeutic cloning involves producing embryonic stem cells for medical research or treatment. These cells can develop into any type of tissue and are genetically identical to the donor.
Cell lines in research are often derived from a single cell, making them clonal. However, during cell division, mutations and gene expression changes can lead to cellular differentiation. Although the cells originate from a common ancestor, they are not always genetically or functionally identical.
Stem cells are undifferentiated cells capable of giving rise to various cell types. While daughter cells may be derived from the same stem cell, they become distinct as they specialize into tissue-specific cells.
Cloning, especially reproductive cloning in humans, raises ethical concerns including identity, individuality, and the potential for misuse. These issues are widely debated in the fields of bioethics, law, and public policy.
