What is Clone?
[[File:Dolly clone.svg|thumb|Dolly clone]] A '''clone''' is any [[cell]] or individual which is identical to another. 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> 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. In [[genetics]] and [[cell biology]], cloning refers especially to the [[DNA]] sequence, and by implication all the other [[macromolecule]]s. 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. The [[laboratory]] copying of a molecule to produce exact copies is also called cloning. == Not quite so identical == 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 |title=Some causes of genotypic and phenotypic discordance in monozygotic twin pairs |journal=American Journal of Medical Genetics |year=1996 |volume=6