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Cloning is the process of creating an identical copy of an original. A clone in the biological sense, therefore, is a single cell (like bacteria, lymphocytes etc.) or multi-cellular organism that is genetically identical to another living organism. Sometimes this can refer to "natural" clones made either when an organism reproduces asexually or when two genetically identical individuals are produced by accident (as with identical twins), but in common parlance the clone is an identical copy by some conscious design. Also see clone (genetics).

The term clone is derived from κλων, the Greek word for "twig". In horticulture, the spelling clon was used until the twentieth century; the final e came into use to indicate the vowel is a "long o" instead of a "short o". Since the term entered the popular lexicon in a more general context, the spelling clone has been used exclusively.


Cloning in biology


Cloning a gene means to extract a gene from one organism (for example by PCR) and insert it into a second organism (usually via a vector), where it can be used and studied. Cloning a gene sometimes can refer to success in identifying a gene associated with some phenotype. For example, when biologists say that the gene for disease X has been cloned, they mean that the gene's location and DNA sequence has been identified, although the ability to specifically copy the physical DNA is a side-effect of its identification. A related technique called subcloning refers to transfering a gene from one plasmid into another for further study.


Cloning a cell means to derive a population of cells (a clonal population) from a single cell. This is an important in vitro procedure when the expansion of a single cell with certain characteristics is desired, for example in the production of gene-targeted ES cells. Most individuals began as a single cell (a zygote) and are therefore the result of clonal expansion in vivo.

Cloning an organism broadly means to create a new organism with the same genetic information as a cell from an existing one. In a modern context, this can involve somatic cell nuclear transfer in which the nucleus is removed from an egg cell and replaced with a nucleus extracted from a cell of the organism to be cloned (currently, both the egg cell and its transplanted nucleus must be from the same species). As the nucleus contains (almost) all of the genetic information of a lifeform, the "host" egg cell will develop into an organism genetically identical to the nucleus "donor". However, this process does not conserve the mitochondrial genome unless the nucleus and oocyte donor were the same individual. Thus, nuclear transfer clones are not clones in the strictest sense because the mitochondrial genome is not the same as that of the nucleus donor cell from which it was produced. This may have important implications for cross-species nuclear transfer in which nuclear-mitochondrial incompatibilities may lead to inviability.



Natural clones

Cloning exists in nature in some species and is refered to as parthenogenesis. An example is the "Little Fire Ant," Wasmannia auropunctata, which is native to Central and South America but has spread throughout many tropical environments.[1] In this species, circumstantial evidence from microsatellite DNA suggest that both queens and males may reproduce clonally in one population in Suriname.

Species cloned

The modern cloning techniques involving nuclear transfers have been successfully performed on several species. Land mark experiments in chronological order:

For a complete list see: List of animals that have been cloned

Health aspects

However, the success rate has been very low: Dolly was born after 276 failed attempts; 70 calves have been created from 9,000 attempts and one third of them died young; Prometea took 328 attempts, and, more recently, Paris Texas was created after 400 attempts. Notably, although the first clones were frogs, no adult cloned frog has yet been produced from a somatic adult nucleus donor cell.

A surprising development to do with aging resulted from finds that Dolly was apparently subject to accelerated aging. Aging of this type is thought to be due to telomeres, regions at the tips of chromosomes which prevent genetic threads fraying every time a cell divides. Over time telomeres get worn down until cell-division is no longer possible - this is thought to be a cause of aging. However, when researchers cloned cows they appeared to age more slowly than expected. Analysis of the cow's telomeres showed they had not only been 'reset' to birth-length, but they were actually longer - suggesting these clones would live longer life spans than normal cows (but many have died young after excessive growth). Researchers think that this could eventually be developed to reverse aging in humans. Although some work has been performed on telomeres and aging in nuclear transfer clones, the evidence is contradictory and does not support any generalizable link.

Therapeutic cloning is the procedure for creating stem cells genetically compatible with the patient. Therapeutic cloning might provide a way to grow organs in host carrier, which become completely compatible with the original. Host carrier growing poses a risk of trans-species diseases if the host is of a different species (e.g. a pig.)

Human cloning

Main article: Human cloning

Artificial human cloning is a subject of great controversy regarding its ethical and practical consequences. Some believe human reproductive cloning is unethical. A number of groups are working on or have already produced human embryo clones [4].

British scientists have cloned a human embryo that lived for 5 days. Dr. Woo-Suk Hwang and colleagues from Korea reported on 17 June 2005 (Science 308: 1738) the successful cloning of 11 human embryonic stem cell lines by transferring nuclei from fibroblasts of patients into human denucleated eggs. Although Hwang had earlier reported the creation of a cloned stem cell line by transferring the nucleus of a person into her own eggs, these represent the first time that human embryonic stem cells were created by transfer of nuclei from other people. Of the 11 human embryonic stem cell line, 9 were from people with spinal cord injury.

Natural clones are called identical twins.

Cloning extinct species

Cloning, or more precisely, the reconstruction of functional DNA from extinct species has, for decades, been a dream of some scientists. The possible implications of this were dramatized in the novel by Michael Crichton and high budget Hollywood thriller, called "Jurassic Park". In real life, one of the most anticipated targets for cloning was once the Woolly mammoth, but attempts to extract DNA from frozen mammoths have been unsuccessful.

In 2000, a cow named Bessie gave birth to a cloned Asian guar, an endangered species; this provided hope that similar techniques (using surrogate mothers of another species) might be used to clone extinct species; in anticipation of this possibility, the last bucardo, a Spanish mountain goat, was frozen immediately after it died (from illness after birth). Researchers are also considering cloning endangered species such as the giant panda, ocelot, and cheetah[5].

In 2002, geneticists at the Australian Museum announced that they had replicated DNA of the Thylacine (Tasmanian Tiger), extinct about 65 years previous, using polymerase chain reaction (PCR)[6]. However, on February 15, 2005 the museum announced that it was stopping the project after tests showed the specimens' DNA had been too badly degraded by the (ethanol) preservative. Most recently, on May 15, 2005, it was announced that the project would be revived, with new participation from researchers in New South Wales and Victoria.

One of the continuing obstacles in the attempt to clone extinct species is the need for nearly perfect DNA. Furthermore, if animals were cloned from one individual, the significant problem of lack of genetic diversity would still remain in the attempt to establish a breeding population.

Commercial cloning

While the promise of cloning extinct species has been a long standing justification for the development of cloning, there are many other applications, such as cloning animals (eg. cattle and horses), which appears to offer a much faster and more efficient way of propagating desirable genes (as chosen by humans) than traditional breeding.

Another application which has recently become feasible is the cloning of pets. The company Genetic Savings and Clone was established to provide such a service, using chromatid transfer which is arguably more effective than nuclear transfer, with Little Nicky being the first pet cloned by the company after the death of the original cat. The procedure is still very expensive and has little demand. However, demand could be generated from unexpected quarters, such as Hollywood movies studios, which could seek to store genetic samples of "animal actors" for the purpose of creating a clone to replace the original animal in a sequel [7].

Cloning in Fiction

Cloning has been widely explored in science-fiction.

  • Star Wars (film series): A race of aliens called Kaminoans use an accelerated cloning technique to create an army of over a million human soldiers that participate in a galaxy-wide conflict known as the Clone Wars.
  • The Boys From Brazil (novel and film adaptation)
  • Brave New World: the population is grown. The lower castes are cloned from a single egg (Bokanofskyfied).
  • The 6th Day: a film whose main themes are clones (such as the protagonist 'being' one) and branching ethical cloning problems.
  • The Island: another film about the ethics of cloning. Follows the story of clones grown in a secret complex for the sole purpose of killing them and using their organs as replacements for their original versions in the real world, all while being convinced they are living purposeful lives.
  • Jurassic Park:cloning of dinosaurs by the use of prehistoric insects that sucked their blood.(DNA cloning of the blood)
  • The House of the Scorpion:young adult novel following the life of a clone named Matteo Alacran.
  • Metal Gear Solid
  • "The Clone" by H.G.Wells
  • "Cloning": Novel by David Shear, first published in 1972, about a man who discovers he is a clone. His mind and body are taken over by the psyche of his genetic twin whom he never knew and died a violent death.
  • "Godsend"

External links and references

^  "Bizarre stand-off in battle of the sexes" New Scientist, July 2, 2005

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