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Cloning is the process of creating an identical copy of an original. A clone in the biological sense, therfore, is a multi-cellular organism that is genetically identical to another living organism. Sometimes this can refer to "natural" clones made when an organism reproduces asexually, but in common parlance the clone is an identical copy by some conscious design.

The word was coined by the British geneticist J. B. S. Haldane in 1963, and is derived from the Greek word for "twig".

In biology, cloning refers either to copying a single gene, or a whole organism.

• Cloning a gene means to extract a gene from one organism (for example, by PCR) and to insert it into a second organism (usually via a vector), where it can be used and studied.
• Cloning an organism means to create a new organism with the same genetic information as an existing one. This can be done by removing the nucleus from an egg cell and replacing it with a nucleus extracted from some 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".

This technique has been successfully performed on several species, such as frogs, mice, sheep, and cattle (the most famous example being the sheep "Dolly"). However the success rate is 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. With certain species such as dogs, rats and horses no successful clones have been created at all. Many people believe that attempts to perform human cloning would be unethical, but some scientists have publicly announced their intention to do so. Some believe the Chinese may have already done so.

A surprising development to do with aging resulted from finds that Dolly was apparently born old, she developed arthritis aged six. This is thought to be due to telomeres. These are 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 be younger than they should be. 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.

The Raelites have announced that they intend to practice human cloning, and have a list of candidates; their intention is to produce human immortality by cloning and uploading the personalities into the clone. There does not currently exist any method for doing this, nor do many scientists think it will possible in the near future, so Raelites are not generally taken seriously.

The controversial physician Severino Antinori claimed in Movember 2002 that a project to clone human beings has succeeded, with the first human clone due to be born in January 2003. His claims were received with scepticism from many observers.

See also : Human cloning