Clone

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A clone is any cell or individual which is identical to another.

In biology, cloning is the process of producing one or more genetically-identical individuals. With whole individuals, it usually means the deliberate production of an identical copy. This was first achieved in mammals with the famous Dolly the sheep. Human identical twins are natural clones. So are the offspring of asexual reproduction, and any parthenogenetic reproduction which does not involve meiosis.[1]

Cloning is natural to some animals, but rare in mammals. An exception is the Nine-banded armadillo, which normally gives birth to identical quadruplets.

In genetics and cell biology, cloning refers especially to the DNA sequence, and by implication all the other macromolecules.

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 cells, so they are clones only in the sense of being derived from the same mother cell.

The laboratory copying of a molecule to produce exact copies is also called cloning.

Not quite so identical[change | change source]

Although clones start off identical, they may not stay that way. Identical twins always have slightly different phenotypes.[2][3]

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 foetal development. This is caused by mutations (or copy errors) taking place in the DNA of each twin after the splitting of the embryo.[4] 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.

Another cause of difference between monozygotic twins is 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.[5] 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.[6][7][8]

Species cloned[change | change source]

  • 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.[9]
  • 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.[10]
  • 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.[11]
  • Monkey: (2000) Tetra, from embryo splitting.[12][13]
  • Gaur: (2001) was the first endangered species cloned.[14]
  • Cattle: Alpha and Beta males 2001 and 2005, Brazil.[15]
  • Cat: CopyCat "CC" (female, late 2001), Little Nicky, 2004, was the first cat cloned for commercial reasons.[16]
  • Dog: (2005) Snuppy, a male Afghan hound was the first cloned dog.[17]
  • Rat: (2003) Ralph, the first cloned rat.[18]
  • Mule: (2003) Idaho Gem, a john mule, was the first horse-family clone.[19]
  • Horse: (2003) Prometea, a Haflinger female, was the first horse clone.[20]
  • 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.[21]
  • Camel: (2009) The first cloned camel.[22]

References[change | change source]

  1. If there is crossing over between the paired chromosomes in the cells leading up to the egg, then the eggs will not be identical.
  2. Machin, G.A. 1996. Some causes of genotypic and phenotypic discordance in monozygotic twin pairs. American Journal of Medical Genetics 61 (3): 216–228. doi:10.1002/(SICI)1096-8628(19960122)61:3<216::AID-AJMG5>3.0.CO;2-S . PMID 8741866 .
  3. Schmid 2000.. "Prenatal diagnosis of heterokaryotypic mosaic twins discordant for fetal sex.". Prenat Diagn 20 (12): 999–1003. PMID 11113914 .
  4. "Identical twins are genetically different, research suggests | Mail Online". Dailymail.co.uk. 2012-11-13. http://www.dailymail.co.uk/sciencetech/article-2232148/Identical-twins-genetically-different-research-suggests.html. Retrieved 2013-09-16.
  5. "Epigenetic differences arise during the lifetime of monozygotic twins". Proc. Natl. Acad. Sci. U.S.A. 102 (30): 10604–9. 2005. doi:10.1073/pnas.0500398102 . PMC 1174919 . PMID 16009939 .
  6. Segal, Nancy L. (1999). Entwined lives: twins and what they tell us about human behavior. New York: Dutton. ISBN 0-525-94465-6 . OCLC 40396458 .
  7. Plomin, Robert (2001). Behavioral genetics. New York: Worth Pubs. ISBN 0-7167-5159-3 . OCLC 43894450 .
  8. Mandler,G. (2001) Apart from genetics: What makes monozygotic twins similar? Journal of Mind and Behavior. 22, 147-159.
  9. "Bloodlines timeline". PBS.org. http://www.pbs.org/bloodlines/timeline/text_timeline.html.
  10. "Кто изобрел клонирование?". Archived from the original on 2004-12-23. http://web.archive.org/web/20041223221951/http://www.whoiswho.ru/russian/Curnom/22003/cl.htm. (in Russian)
  11. McLaren A (2000). "Cloning: pathways to a pluripotent future". Science 288 (5472): 1775–80. doi:10.1126/science.288.5472.1775 . PMID 10877698 .
  12. CNN: Researchers clone monkey by splitting embryo 2000. Retrieved 2008-08-05.
  13. Dean Irvine (2007). "You, again: are we getting closer to cloning humans? - CNN.com". Edition.cnn.com. http://edition.cnn.com/2007/WORLD/europe/11/16/ww.humancloning/index.html?iref=allsearch. Retrieved 2010-08-04.
  14. "First cloned endangered species dies 2 days after birth". CNN. 2001. http://archives.cnn.com/2001/NATURE/01/12/cloned.gaur/index.html. Retrieved April 30, 2010.
  15. Camacho, Keite. Embrapa clona raça de boi ameaçada de extinção. Agência Brasil. 2005 (in Portuguese) Retrieved 2008-08-05
  16. "Americas | Pet kitten cloned for Christmas". BBC News. 2004. http://news.bbc.co.uk/1/hi/world/americas/4120179.stm. Retrieved 2010-08-04.
  17. "First dog clone". News.nationalgeographic.com. http://news.nationalgeographic.com/news/2005/08/photogalleries/dogclone/. Retrieved 2010-08-04.
  18. "Rat called Ralph is latest clone". BBC News. September 25, 2003. http://news.bbc.co.uk/2/hi/science/nature/3136776.stm. Retrieved April 30, 2010.
  19. Associated Press August 25, 2009 (2009-08-25). "Gordon Woods dies at 57; Veterinary scientist helped create first cloned mule". latimes.com. http://www.latimes.com/news/nationworld/nation/la-me-gordon-woods25-2009aug25,0,5372986.story. Retrieved 2010-08-04.
  20. "World's first cloned horse is born - 06 August 2003". New Scientist. http://www.newscientist.com/article/dn4026-worlds-first-cloned-horse-is-born.html. Retrieved 2010-08-04.
  21. Kounteya Sinha, TNN, Feb 13, 2009, 12.33am IST (2009). "India clones world's first buffalo - India - The Times of India". Timesofindia.indiatimes.com. http://timesofindia.indiatimes.com/India-clones-worlds-first-buffalo/articleshow/4120044.cms. Retrieved 2010-08-04.
  22. Spencer, Richard (2009). "World's first cloned camel unveiled in Dubai". London: Telegraph.co.uk. http://www.telegraph.co.uk/news/newstopics/howaboutthat/5153780/Worlds-first-cloned-camel-unveiled-in-Dubai.html. Retrieved April 15, 2009.