A clone is an organism or group of organisms or cells descended from a single ancestor and having genetic material (DNA, deoxyribonucleic acid) identical to that of the ancestor. Cloning hit the news headlines in 1997 when scientists in Scotland announced they had successfully cloned a sheep, named Dolly, in 1996. Although several other animal species had been cloned in the previous twenty years, it was Dolly that caught the public’s attention. Suddenly, the possibility that humans might soon be cloned jumped from the pages of science fiction stories into the mainstream press. Dolly was the first adult mammal ever cloned.
As of 2010, no human being has yet been cloned but tthical debates over cloning are closely related to debates about other forms of biotechnology that involve the manipulation of DNA.
A clone is a single cell, a group of cells, or an organism produced in a laboratory without sexual reproduction. In effect, the clone is an exact genetic copy of the original source, much like identical twins. There are two types of cloning. Blastomere separation, also called “twinning,” named after the naturally occurring process that creates identical twins, involves splitting a developing embryo soon after the egg is fertilized by sperm. The result is identical twins with DNA from both parents. The second cloning type, called nuclear transfer, is what scientists used to create Dolly. In cloning Dolly, scientists transferred genetic material from an adult female sheep to an egg in which the nucleus containing its genetic material had been removed.
Simple methods of cloning plants, such as grafting and stem cutting, have been used for more than 2,000 years. The modern era of laboratory cloning began in 1958 when the English-American plant physiologist Frederick C. Steward cloned carrot plants from mature single cells placed in a nutrient culture containing Page 327 | Top of Articlehormones, chemicals that play various and significant roles in the body.
The first cloning of animal cells occurred in 1964. In the first step of the experiment, biologist John B. Gurdon destroyed with ultraviolet light the genetic information stored in a group of unfertilized toad eggs. He then removed the nuclei (the part of an animal cell that contains the genes) from intestinal cells of toad tadpoles and injected them into those eggs. When the eggs were incubated (placed in an environment that promotes growth and development), Gurdon found that 1–2 percent of the eggs developed into fertile, adult toads.
The first successful cloning of mammals was achieved nearly twenty years later. Scientists in both Switzerland and the United States successfully cloned mice using a method similar to that of Gurdon. However, the Swiss and American methods required one extra step. After the nuclei were taken from the embryos of one type of mouse, they were transferred into the embryos of another type of mouse. The second type of mouse served as a substitute mother that went through the birthing process to create the cloned mice. The cloning of cattle livestock was achieved in 1988 when embryos from cows were transplanted to unfertilized cow eggs whose own nuclei had been removed.
Since Dolly, the pace and scope of cloning mammals has greatly intensified. In February 2002, scientists at Texas A&M University announced they had cloned a cat, the first cloning of a common domestic pet. Named “CC” (for carbon copy or copycat), the cat is an exact genetic duplicate of a two–year–old calico cat. Scientists cloned CC in December 2001 using the nuclear transfer method. In April 2002, a team of French scientists announced they had cloned rabbits using the nuclear transfer process. Out of hundreds of embryos used in the experiment, six rabbits were produced, four that developed normally and two that died. Two of the cloned rabbits mated naturally and produced separate litters of seven and eight babies
The first human embryos were cloned in 1993 using the blastomere technique that placed individual embryonic cells (blastomeres) in a nutrient culture where the cells then divided into forty-eight new embryos. These experiments were conducted as part of some studies on in vitro (out of the body) fertilization aimed at developing fertilized eggs in test tubes that could then be implanted into the wombs of women having difficulty becoming pregnant. However, these fertilized eggs did not develop to a stage that was suitable for transplantation into a human uterus.
The cloning of cells promises to produce many benefits in farming, medicine, and basic research. In farming, the goal is to clone plants that contain specific traits that make them superior to naturally occurring plants. For example, field tests have been conducted using clones of plants whose genes have been altered in the laboratory by genetic engineering to produce resistance to insects, viruses, and bacteria. New strains of plants resulting from the cloning of specific traits have led to fruits and vegetables with improved nutritional qualities, longer shelf lives, and new strains of plants that can grow in poor soil or even underwater.
A cloning technique known as twinning could induce livestock to give birth to twins or even triplets, thus reducing the amount of feed needed to produce meat. Cloning also holds promise for saving certain rare breeds of animals from extinction, such as the giant panda.
In medicine, gene cloning has been used to produce vaccines and hormones. Cloning techniques have already led to the inexpensive production of the hormone insulin for treating diabetes and of growth hormones for children who do not produce enough hormones for normal growth. The use of monoclonal antibodies in disease treatment and research involves combining two different kinds of cells (such as mouse and human cancer cells) to produce large quantities of specific antibodies. These antibodies are produced by the immune system to fight off disease. When injected into the blood stream, the cloned antibodies seek out and attack disease-causing cells anywhere in the body.
Despite the benefits of cloning and its many promising avenues of research, certain moral, religious, and ethical questions concerning the possible abuse of cloning have been raised. At the heart of these questions is the idea of humans tampering with life in a way that could harm society, either morally or in a real physical sense. Some people object to cloning because it allows scientists to “act like God” in manipulating living organisms.
The cloning of Dolly and the fact that some scientists are attempting to clone humans raised the debate over this practice to an entirely new level. A person could choose to make two or ten or 100 copies of himself or herself by the same techniques used with Dolly. This realization has stirred an active debate about the morality of cloning humans. Some people see benefits from the practice, such as providing a way for parents to produce a new child to replace one dying of a terminal disease. Other people worry about humans taking into their own hands the future of the human race.
Another controversial aspect of cloning deals not with the future but the past. Could Abraham Lincoln or Albert Einstein be recreated using DNA from a Page 328 | Top of Articlebone, hair, or tissue sample? If so, perplexing questions arise about whether this is morally or ethically acceptable? While it might ultimately be possible to create genetic duplicates, the clone would not have the same personality as the original Lincoln. This is because Lincoln, like all people, was greatly shaped from birth by his environment and personal experiences in addition to his genetic coding. And although CC, the cloned calico cat, is a genetic duplicate of her mother, she nevertheless has a different color pattern of fur than her mother. This is because environmental factors strongly influenced her development in the womb.
Since the movie “Jurassic Park” was released in 1993, there has been considerable public discussion about the possibility of cloning dinosaurs and other prehistoric or extinct species. In 1999, the Australian Museum in Sydney, Australia, announced scientists were attempting to clone a thylacine (a meat–eating marsupial related to kangaroos and opossums). The species has been extinct since 1932 but the museum has the body of a baby thylacine that has been preserved for 136 years. The problem is that today’s cloning techniques are possible only with living tissue. The project was abandoned in 2005 after the DNA proved too degraded to construct a DNA library.
See also Genetic engineering .
Brown, Terry. Gene Cloning and DNA Analysis: An Introduction. 5th ed. Oxford, UK: Blackwell Science, 2006.
Caplan, Arthur and Glenn McGee, eds. The Human Cloning Debate. Berkeley: Berkeley Hills Books, 2006.
Harris, John. On Cloning. London and New York: Routledge, 2004.
Van Laar, Relinde. Cloning and Stem Cell Research Legal Documents: An Overview of Research and Studies in Stem. Tilburg: Wolf Legal Publishers, 2009.
Wilmut, Ian, and Roger Highfield. After Dolly: The Promise and Perils of Cloning. New York: W. W. Norton, 2007.
Dinnyes, A., and A. Szmolenszky, “Animal Cloning by Nuclear Transfer: State-of-the-Art and Future Perspectives.” Acta Biochimica Polonica 52, no. 3 (March 2005): 585–588.
The Human Genome Project. “Human Genome Project: Cloning.” http://www.ornl.gov/sci/techresources/Human_Genome/elsi/cloning.shtml (accessed October 20, 2010).
Ken R. Wells
Gale Document Number: GALE|CX1918700308