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Example research essay topic: Genetically Identical Identical Twins - 1,390 words

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Of 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 which is the fertilized egg. Likewise, many tumours are clones, derived from one aberrant cell which no longer obeys the normal rules of growth control.

The offspring of organisms which reproduce asexually, like corals, are also clones; as are identical twins produced by the natural, or sometimes deliberate, splitting of a single embryo. Members of a clone are genetically identical and genetic identity has given cloning an additional more technical meaning: namely the procedures used to create a new organism whose genetic constitution is a replica of another existing individual. Such a feat can be achieved by substituting the nucleus, which contains the genes, from one of the cells making up that individual's body, for the nucleus of a fertilized egg. Since our genes dictate to a large extent what we look like, how we behave and what we can and cannot do, having identical genes, as identical twins do, ensures something more than mere similarity. Novelists and film makers have not been slow to exploit the imagery afforded by cloning. Limitless numbers of identical beings manufactured from existing or previous generations has obvious dramatic potential, although seldom of a reassuring nature.

Clones traverse the cinema screen as crowds of dehumanized 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 pennyworth. 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 1960 s 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 sophistication's of the modern laboratory. The word 'clone' comes from the Greek known, 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, of identical genetic constitution, will sprout.

Deliberate cloning is as old as horticulture itself. Thousands of years before anyone understood the physical nature of heredity, specific genetic constitutions were preserved through cloning because they bestowed on the plant desirable qualities such as disease-resistance, high yield and predictable growth. Cloning is as important to the production of fine wine, the supply of rubber and the fruit harvest as it is to the variety of an English country garden. Furthermore, natural cloning is not confined to plants: microbes and some insects frequently propagate themselves by producing genetically identical offspring without recourse to sex.

The toothless mammal, the armadillo, gives birth not to identical twins but to genetically identical octuplet's: every litter a batch of eight clones. There is nothing a priori unnatural about cloning. Apart from facilitating plant propagation what are the advantages of generating genetically identical organisms? As with plants, a stable mixture of robustness and productivity is desirable in all agricultural and commercially important animal stock. Centuries of selective breeding have been applied to produce particular breeds with a highly selected genetic composition aimed at ensuring predictable performance. This applies as much to the quest for healthy high milk-yielding cows, or sheep with particularly luxuriant wool, as to breeding the fastest racehorse or producing the supreme champion at Crufts.

The genealogy of Derby winners is a masterpiece of human design. The very diversity of dogs is largely attributable to human intervention. All dogs, be they Great Danes or Chihuahuas, belong to a single species, but over the millenniums man has channelled different canine characteristics into the vastly different strains we see today. Specific desirable features have been accentuated by persistent inbreeding, mating close relatives who are already genetically similar such as brother and sister, or father and daughter, to create even greater genetic homogeneity.

As we know this is not always a wholly benign process. For example, the features of Pugs so loved by their owners are without question a serious handicap to the dog when it comes to breathing. Likewise, inbreeding to enhance desirable attributes can sometimes also increase the likelihood of genetic disease. Genes causing hip dysplasia have been carried along with genes defining the handsome lines of Labradors. Disadvantages aside, the huge array of dog breeds illustrates that striving for genetic similarity and stability, contrary to popular belief, does not necessarily decrease diversity but actually often generates greater variety. In biological research, using genetically identical material, be it cells in a dish or whole organisms, is often essential for standard ising experiments.

Only when differences in genetic effects can be ruled out can the response to a certain drug or a particular infection be interpreted unambiguously. Ironically, understanding the mechanisms which cause the body to reject transplants of genetically dissimilar tissue, required generations of inbreeding to produce different inbred strains of mice each composed of essentially genetically identical individuals. Only then could the response to foreign tissue be scrutinised rationally. For reasons of survival, commerce, scientific endeavour and sometimes just whimsy, and for a very long time, selective breeding has been used to achieve slowly but surely more or less the same ends that cloning can.

However, there are two major differences between cloning and inbreeding. Firstly, inbreeding takes a long time to ensure the requisite genetic identity. Secondly, it can only take advantage of genes already present in the organism. In theory cloning provides an alluring short cut to amplifying the number of anima...


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Research essay sample on Genetically Identical Identical Twins

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