Cloning (See bottom of page for how to cite this article) The word "clone" comes from the Greek word meaning "twig." It refers to the practice of taking plant cuttings. Such cuttings produce new plants identical to their parent. In genetics, cloning refers to methods that produce genetically identical cells or organisms. Natural Clones Nature produces many clones. Bacteria, for example, reproduce through cloning. And the Greeks were right. Plant cuttings are genetic clones. Indeed, cloning is common in the plant kingdom. But it is rare among animals. It is seen in invertebrates. These simple animals lack backbones. Some, such as flatworms, often reproduce by cloning. In higher animals, identical twins represent natural clones. They develop from the same fertilized egg. They are clones of each other. But they are not clones of their parents. Artificial Clones Genetic technology is one of science's fastest-growing fields. Artificial cloning stands out as one of its most revolutionary applications. It involves the creation of offspring genetically identical to one parent. This bypasses normal sexual reproduction, which mixes the genes of two parents. Breeding Programs Cloning is of particular interest to plant and animal breeders. Throughout history, people have bred superior crops and livestock. Such selective breeding is used to enhance desirable traits. Examples include milk production in cows and speed in race horses. Breeders have long sought a way to reproduce their "star performers." Sexual reproduction is less than ideal. It mixes genes in unpredictable ways. Cloning, by contrast, preserves a complete set of genes. This is of special interest to those who produce transgenic animals. Such animals are genetically engineered by inserting certain human genes into their cells. Examples include goats, sheep, and other mammals that secrete human hormones in their milk. These hormones are used as medicinal drugs. Clearly, such transgenic animals are valuable. But their natural offspring do not reliably inherit their transgenic traits. Cloned offspring would. Cloning Techniques Typically, animal cloning begins by retrieving a complete set of genes. This can be done by removing the nucleus from an adult cell. This donor nucleus is transferred into a fertilized egg. This egg can be from another animal. But first the egg's own nucleus must be removed. If all goes well, the egg develops into a clone with genes identical to the animal that supplied the nucleus. This type of cloning is called nuclear transplantation. It was first used successfully in 1952. Early animal clones included frogs and other amphibians. Mammals proved more of a challenge. A milestone was reached in 1996. That year, Scottish researchers cloned a sheep. Specifically, they used genes from the mammary cells of an adult ewe. The resulting lamb was named Dolly. She matured normally and even produced a lamb—the natural way. Since then, many other mammals have been cloned. They include mice, cows, pigs, rats, mules, and horses. In 2001 the first cat was cloned. A dog followed in 2003. These events were of special interest to pet owners. Some have since paid high prices to clone their beloved companions. In fact, cloned animals are not perfect copies of their parent. They can differ in both appearance and personality. Genes may code for traits. But other forces influence how these traits are expressed. Complications Cloning is far from a perfect science. In some cases, cloned animals are born with abnormalities. Cloned calves, for example, often have defective organs. Analysis shows that some of their genes do not function normally. Clones may also show signs of premature aging. And some are prone to various cancers. Objections Cloning also raises ethical issues. The most controversial is the idea of human cloning. Will people be tempted to make copies of themselves? Will they try to reproduce a dead or dying child? In 2001 a company announced that it had used cloning to produce human embryos. The company's stated goal was to create stem cells, not babies. Nonetheless, their creation shocked many people. In this case, the embryos died after several days. But in theory, the technology now exists to clone people. Many people find the prospect of cloning humans morally wrong. Several countries have enacted laws against it. Other Uses Cloning has uses beyond reproduction. Another goal is to clone organs. This could help solve the chronic shortage of donated organs. Such donations are needed to save the lives of people with organ failure. But the supply falls far short of the need. Most objections to organ cloning arise from its use of cells from human embryos. In the process the embryo is destroyed. This remains objectionable to people who consider embryos as humans deserving protection. Recent advances may eliminate this problem. Researchers are finding ways to use adult stem cells instead of embryonic ones. These adult cells remain in an immature state. More research is needed to perfect their use in cloning. How to cite this article: MLA (Modern Language Association) style: "Cloning." The New Book of Knowledge. Grolier Online, 2013. Web. 16 Jan. 2013. ™ & © 2013 Scholastic Inc. s Reserved