The term “cloning” is used by scientists to describe many different processes that involve making copies of biological material, such as a gene, a cell, a plant or an animal. The cloning of genes, for example, has led to new treatments developed by the biotechnology industry for diseases such as diabetes and hemophilia. In the context of this report, a human embryo produced via cloning involves the process called somatic cell1 nuclear transfer (SCNT). In SCNT, the nucleus of an egg is removed and replaced by the nucleus from a mature body cell, such as a skin cell. In cloning, the embryo is created without sexual reproduction: there is no joining of egg and sperm.
Concern over the possibility of producing a human clone increased with the announcement on February 24, 1997, that scientists in Scotland had used SCNT in 1996 to produce the first cloned adult mammal, Dolly, the sheep. Ian Wilmut’s group at the Roslin Institute in Edinburgh removed the nucleus from a sheep egg and replaced it with the nucleus of a mammary gland cell from an adult sheep. The resulting embryo was then transferred to the uterus of a surrogate sheep. A total of 277 such embryos were transferred, but only one lamb was born.2 Analyses of Dolly’s genetic material confirmed that she was derived from the sheep mammary cell. Dolly was euthanized on February 14, 2003, after developing a lung infection. Although some claim that her somewhat early death at six years was related to being a clone, scientists at the Roslin Institute believe her ailment may be due to the fact that she was raised indoors (for security reasons) rather than as a pastured sheep, which can live to 11 or 12 years of age.3
Although scientists have been successful in using SCNT to produce other animals (such as a cat, goat, cow, horse, mule, pig, mouse, and rabbit), the efficiency of the procedure is still very low and frequently results in abnormal development. Proponents maintain that one day cloning may be very useful for a number of agriculture applications, including the improvement of livestock. Currently, cloned mice are used for basic research on human health applications.
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A somatic cell is a body cell, as opposed to a germ cell, which is an egg or sperm cell.
2 I. Wilmut et al., “Viable Offspring Derived from Fetal and Adult Mammalian Cells.” Nature, vol. 385, Feb. 27, 1997, pp. 810-813.
3 G. Kolata, “First Mammal Clone Dies; Dolly Made Science History,” New York Times, Feb. 15, 2003, p. A4.