The possibility of human cloning, raised when Scottish scientists at Roslin Institute created the first successful animal clone of a sheep, "Dolly."
             Cloning refers to copying genes and other pieces of chromosomes to generate enough identical material for further study. Two other types of cloning
             produce complete, genetically identical animals. Blastomere separation (sometimes called "twinning" after the naturally occurring process that creates identical twins) involves splitting a developing embryo soon after fertilization of the egg by a sperm (sexual reproduction) to give rise to two or more embryos. The resulting organisms are identical twins (clones) containing DNA from both the mother and the father. Dolly, on the other hand, is the result of another type of cloning that produces an animal carrying the DNA of only one parent. Using somatic cell nuclear transfer, scientists transferred genetic material from the nucleus of an adult sheep's udder cell to an egg whose nucleus, and thus its genetic material, had been removed. (All cells that are not egg or sperm cells are somatic cells.) One goal of this and similar research is to develop efficient ways to alter animals genetically and reproduce them reliably. Alterations have included adding genes (such as those for human proteins) to create drug-producing animals as well as inactivating genes to study the effects and possibly create animal models of human diseases. Cloning technology also may someday be usedin humans to produce whole organs from single cells or to raise animals having genetically altered organs suitable for transplanting to humans.
             Not all cloning would involve creating an entirely new human being. Cloning is seen as a possible way to aid some people who have severe medical problems. One potential use of cloning technology would involve creating a human repair kit. In other words, scientists could clone our cells and fix mutated genes that cause diseases. In a...