CloningOf all the terms coined by scientists which have entered popular vocabulary, 'clone' has become one of the more emotive. Strictly speaking a clone refers to one or more offspring derived from a single ancestor, whose genetic composition is identical to that of the ancestor. No sex is involved in the production of clones, and since sex is the normal means by which new genetic material is introduced during procreation, clones have no choice but to have the same genes as their single parent. In the same way, a clone of cells refers simply to the descendants of a single parental cell. As such, adult organisms can be viewed as clones because all their parts stem from the single cell wh ...view middle of the document...
Clones traverse the cinema screen as crowds of dehumanised humans destined for monotonous drudgery, as invincible armies of lookalikes from outer space, as replicas of living megalomaniacs and, in the ultimate fantasy, as the resurrected dead - troupes of little Hitlers and herds of rampaging dinosaurs. Of course, this is science fiction. Nonetheless there is just a whiff of plausibility, a whisker of scientific credibility; enough to plant an indelible vision of what might be, or even what could be.So it is easy to understand why the arrival earlier this year of Dolly, the sheep developed from an egg whose own genes had been replaced by those from an adult udder cell, was seen as the first incarnation of a sinister future. Dolly was a clone of the sheep (her genetic mother) who provided the udder cell. The package of genes in the nucleus of that udder cell contained exactly the same repertoire of genes as all the rest of her mother's cells and so Dolly's genetic makeup was to all intents and purposes identical to her mother's. No sperm had had the opportunity to add its genetic pennysworth. However, there was nothing radically new, neither technically nor conceptually, in the way in which Dolly was made. Almost all films and documentaries on cloning still show the same footage, produced more than twenty-five years ago during unsuccessful attempts to clone rabbits, of a nucleus being injected into an egg. What was novel about Dolly was that she was the first unequivocal mammalian clone. Lower vertebrates had been cloned in the early 1960s when it was shown that a nucleus taken from an adult frog cell transplanted to a frog egg whose own nucleus had been destroyed was able to direct the development of that egg into a swimming tadpole. Indeed, it was this experiment that first indicated that the genetic content of all our cells, despite the profound differences between a skin cell and kidney cell, must be more or less the same and retain all the genetic information necessary for an egg to develop into a whole organism.While cloning can offer the scientist important answers to fundamental questions about our genes, it has a much older and very natural history which long precedes the sophistications of the modern laboratory. The word 'clone' comes from the Greek klwn, meaning twig, and there is a very good reason for this. For example, every chrysanthemum plant you buy at a Garden Centre is a clone of some distant and probably long dead chrysanthemum which once supplied a side-shoot for rooting. Likewise, whenever you divide an overgrown shrub or successfully cultivate a houseplant cutting you are cloning. In each case you are deliberately propagating a copy of the parent, and eventually over successive years and many hours in the greenhouse, producing a multitude of plants (clones) all genetically identical to the prized parent. Elm trees and other suckering plants clone themselves naturally, sending out subterranean roots from which new plants,...
