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Cloning is the creation of an individual that is a genetic replica of another individual. The process transfers a nucleus from a somatic nonreproductive cell into an "enucleated" fertilized egg, one that has had its own nucleus destroyed or removed. The genes in the transferred nucleus then direct the development of a complete organism from the altered fertilized egg. Two individuals who are clones have identical genes in their cell nuclei, but differ in characteristics that are acquired in other ways.

Cloning is a natural phenomenon in species as diverse as armadillos, poplar trees, aphids, and bacteria. Identical twins are clones. Biologists have been cloning some organisms, such as carrots, for decades. Attempts to clone animals have been far less successful. They began long before the February 1997 announcement of the birth of Dolly, a sheep cloned from a mammary gland cell nucleus of a six-year-old sheep.

Oxford University developmental biologist John Gurdon cloned frogs in the 1960s, but in a limited way. He showed that a nucleus from a tadpole's intestinal lining cell could be transferred to an enucleated fertilized egg and support development to adulthood, and that a nucleus from an adult cell could support development as far as the tadpole stage. However, he was unable to coax a nucleus from an adult amphibian's cell to support development all the way to adulthood. In the 1980s several companies tried to commercialize cloning of livestock from nuclei taken from embryos or fetuses. The efforts failed because the cloned animals were nearly always very unhealthy newborns and did not survive for long. Currently, livestock cloning is limited to research, although some companies offer tissue preservation services in anticipation of future advances in commercial livestock cloning. There is no reason to believe that human clones would fare any better in terms of health or survivability than most cloned animals do.

Ethical concerns about whether an action is "right" or "wrong" are often clouded by subjectivity, emotion, and perspective. Cloning members of an endangered species, for example, is generally regarded as a positive application of the technology, whereas attempting to clone an extinct woolly mammoth from preserved tissue elicits more negative responses, including that this interferes with nature. A project at Texas A&M University, funded by a dog lover wishing to clone a beloved deceased pet, announced the first successful cloning of a domestic animal, a cat, in February 2002. Cloning pets when strays crowd shelters might be seen as unethical. A different set of ethical issues emerges when considering the cloning of humans, which a few scientists and physicians have proposed doing outside of the United States.

The first cloned cat, named "cc," (short for "copycat") is proudly displayed by doctors Mark Westhusin (right) and Tae Young (left) of the College of Veterinary Medicine at Texas A&M University on Febuary 8, 2002.

Bioethics is concerned with the rights of individuals, such as the right to privacy and the right to make informed medical decisions. It is difficult to see how these issues would apply to cloning, unless someone was forced or paid to provide material for the procedure, or if an individual was cloned and not informed of his or her origin. Ethical objections to cloning seem to focus more on the fact that this is not a normal way to have a baby. Accordingly, the U.S. House of Representatives voted overwhelmingly on July 31, 2001 to pass legislation that would outlaw human cloning for any reason. However, the broadness of this action may impede other types of medical research, thus introducing a different bioethical dilemma.

The legislation seeks to ban all human cloning, both "reproductive cloning" that would be used to create a baby, and "therapeutic cloning." In therapeutic cloning, a nucleus from a somatic cell is transferred to an enucleated donor egg, and an embryo is allowed to develop for a few days. Then, cells from a part of the embryo called the inner cell mass are used to establish cultures of embryonic stem cells that are genetically identical to the individual who donated the somatic cell nucleus.

If this person has a spinal cord injury or a neurodegenerative disease, the embryonic stem cells might specialize into needed neural tissue. To treat muscular dystrophy, the cells might be coaxed to differentiate into muscle-cell precursors. Such tailored embryonic stem cells would have many applications, and a person's immune system would not reject what is essentially its own tissue. Some people argue that therapeutic cloning violates the rights of early-stage embryos; others argue that banning this research violates the rights of people who might benefit from embryonic stem cell therapy.

According to the bill's ban on producing or selling "any embryo produced by human cloning," scientists caught in the act could expect a fine of up to $1 million or ten years in prison. Proposals to exempt therapeuticcloning were defeated. The criminalization of basic research is unprecedented: Before 2001, bans on using embryonic stem cells applied only to federally funded research, and work using a small number of previously existing stem cell lines was permitted. Since the 2001 ruling, some researchers have moved to nations that permit them to derive new embryonic stem cell lines. Stem cells that are normal parts of adult bodies are being investigated as alternative sources of replacement tissues.

The premise that a clone is an exact duplicate of another individual is flawed, and so if the intent of cloning is to create such a copy, it simply will not work. For example, the tips of chromosomes, called telomeres, shorten with each cell division. A clone's telomeres are as short as those from the donor nucleus, which means that they are "older" even at the start of the clone's existence. DNA in the donor nucleus has also had time to mutate, that is to say, it has had time to undergo modification from its original sequence, thus distinguishing it genetically from other cells of the donor. A mutation that would have a negligible or delayed effect in one cell of a many-celled organism, such as a cancer-causing mutation, might be devastating if an entire organism develops under the direction of that nucleus. Finally, the clone's mitochondria, the cell organelles that house the reactions of metabolism and contain some genes, are those of the recipient cell, not the donor, because they reside in the cytoplasm of the egg. Mitochondrial genes, therefore, are different in the clone than they are in the nucleus donor. The consequences of nuclear and mitochondrial genes from different individuals present in the same cell are not known, but there may be incompatibilities.

Perhaps the most compelling reason why a clone is not really a duplicate is that the environment affects gene expression. Cloned calves have different color patterns, because when the animals were embryos, the cells that were destined to produce pigment moved in different ways in each calf. For humans, consider identical twins. Nutrition, stress, exposure to infectious diseases, and other environmental factors greatly influence our characteristics. For these reasons, cloning a deceased child, the application that most would-be cloners give for pursuing the technology, would likely lead to disappointment.

Bioethical concerns over cloning may be moot, because the procedure is extremely difficult to do. Dolly was one of 277 attempts; Cumulina, the first cloned mouse, was among 15 liveborn mice from 942 tries. Cloning so often fails, researchers think, because it is not a natural way to start the development of an animal. That is, the DNA in a somatic cell nucleus is not in the same state as the DNA in a fertilized ovum. The donor DNA in cloning does not pass through an organism's germ line, the normal developmental route to sperm or egg, where gene activities are regulated as a new organism develops.

Ethical objections to human cloning are more philosophical than they are practical. The very idea of cloning assumes that our individuality can be understood so well that we can duplicate it. If human cloning ever became a reality, that this is not true would become evident. After all, we are more than a mere collection of genes.

Biotechnology: Ethical Issues;; Cloning Genes; Cloning Organisms; Mitochondrial Genome; Stem Cells; Telomere.

Annas, George J. "Cloning and the U.S. Congress." The New England Journal of Medicine 346 (2002): 1599.

Holden, Constance. "Would Cloning Ban Affect Stem Cells?" Science 293 (2001): 1025.

Lewis, Ricki. "The Roots of Cloning." In Discovery: Windows on the Life Sciences. Medford, MA: Blackwell Science, 2000.

Mayor, Susan. "Ban on Human Reproductive Cloning Demanded." British Medical Journal 322 (Jun., 2001): 1566.