Cloning
Cloning is the process of creating an identical copy of an original. A clone'\' in the biological sense, therefore, 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", klōn''.
In biology, cloning is used in two contexts: cloning a gene, or cloning an organism. 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.
Cloning an organism means to create a new organism with the same genetic information as 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, the term clone is used in horticulture to mean all descendants of a single plant, produced by vegetative reproduction. Many horticultural varieties of plants are in effect clones, having been derived from a single individual, multiplied by some process other than sexual reproduction. As an example, some European varieties of grapes represent clones that have been propagated for over two millennia.
The modern cloning techniques involving nuclear transfers have been successfully performed on several species: (in chronological order)
- frogs: time?
- sheep: Dolly
- rhesus monkey: Tetra (female, January 2000)
- pig: 5 Scottish PPL piglets (March 2000), Xena (female, August 2000)
- cattle: Alpha and Beta (males, 2001)
- cat: CopyCat "CC" (female, late 2001)
- mice: over a dozen as of 2002
- mule: Idaho Gem (male, May 2003) and Utah Pioneer (male, June 2003)
- horse: Prometea (female, August 2003)
A surprising development to do with aging resulted from finds that Dolly was apparently born old; she developed arthritis at age six. 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 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.
Human cloning is a subject of great controversy regarding its ethical and practical consequences. A number of groups have made claims that they are working on or have already produced human clones. None of these claims has been independently confirmed. For more on these issues, see the article human cloning.
In computer science, a clone is a computer system based on another company's system and designed to be compatible with it.
When IBM came out with the IBM PC in 1981, other companies such as Compaq decided to put out a clone of the PC as a legal reimplemenatation from the PC's documentation or reverse engineering. As most of the components except the PC's BIOS were publicly available, all Compaq had to do was reverse engineer the BIOS. The result was a machine that had more bang for the buck than the archetypes that the machine resembled. The term "PC clone" fell out of use in the 1990s; the class of machines it now describes are simply called PCs or Intel machines.
Software can also be cloned by reverse engineering or legal reimplementation from documentation or other sources. Software such as MS-DOS's edlin line editor and the Unix operating system have been cloned. The reasons for cloning may include getting around draconian licensing fees or as a curiosity; e.g. because the programmer can.
The Jargon File has this definition for clone:
External Link:
Human cloning
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