To clone is simply to produce an identical copy of something. In the field of biotechnology, however, cloning is a complex term referring to one of three different processes. DNA cloning is used to produce large quantities of a specific genetic sequence and is common practice in molecular biology labs. The other two processes, therapeutic cloning and reproductive cloning, involve the creation of an embryo for research or reproductive purposes, respectively, and have raised concerns about when life begins and who should be able to procure it.
I. DNA Cloning
II. Therapeutic Cloning
III. Reproductive Cloning
DNA cloning, often referred to as recombinant DNA technology or gene cloning, is the process by which many copies of a specific genetic sequence are produced. By creating many identical copies of a genetic sequence through a process known as amplification, researchers can study genetic codes. This technology is used to map genomes and produce large quantities of proteins and has the potential to be used in gene therapy.
The first step in DNA cloning involves the isolation of a targeted genetic sequence from a chromosome. This is done using restriction enzymes that recognize where the desired sequence is and “cut” it out. When this sequence is incubated with a self-replicating genetic element, known as a cloning vector, it is ligated into the vector. Inside host cells such as viruses or bacteria, these cloning vectors can reproduce the desired genetic sequence and the proteins associated with it. With the right genetic sequence, the host cell can produce mass quantities of protein, such as insulin, or can be used to infect an individual with an inherited genetic disorder to give that person a good copy of the faulty gene.
Because DNA cloning does not attempt to reproduce an entire organism, there are few ethical concerns about the technology itself. Gene therapy, however, which is currently at an experimental stage because of safety concerns, has raised ethical debates about where the line falls between what is normal genetic variation and what is a disease.
Somatic cell nuclear transfer (SCNT) is the technique used in both therapeutic cloning and reproductive cloning to produce an embryo that has nuclear genetic information identical to an already existing or previously existing individual.
During sexual reproduction, a germ cell (the type capable of reproducing) from one individual fertilizes the germ cell of another individual. The genetic information in these germ cells’ nuclei combine, the cell begins to divide, and a genetically unique off spring is produced. In SCNT, the nucleus of a somatic cell (the type that makes up adult body tissues) is removed and inserted into a donor germ cell that has had its own nucleus removed. Using electrical current or chemical signals, this germ cell can be induced to begin dividing and will give rise to an embryo that is nearly identical to the individual from which the nucleus came rather than being the result of a combination of two parent cells. This “clone” will not be completely identical to the parent. A small number of genes that reside within mitochondria (small organelles within a cell that convert energy) will have come from the germ cell donor. Therefore the embryo will have nuclear genetic information identical to that of the parent somatic cell but mitochondrial genetic information that is identical to that of the germ cell donor.
SCNT is controversial because it involves the artificial creation of an embryo. Many people who feel that life begins at conception take issue with the technology because a germ cell is induced to divide without first being fertilized.
Similar ethical concerns are raised about therapeutic cloning, also referred to as embryo cloning, which is the production of embryos for the purpose of research or medical treatment. The goal of this procedure is to harvest stem cells from an embryo produced by SCNT.
Stem cells are useful because they are not yet differentiated. Not all cells in the human body are the same; a muscle cell, a bone cell, and a nerve cell have different structures and serve different functions. They all originally arise from stem cells, however, which can be used to generate almost any type of cell in the body. With further research, stem cells may be used to generate replacement cells that can treat conditions such as heart disease, Alzheimer’s, cancer, and other diseases where a person has damaged tissues. This technology might provide an alternative to organ transplantation, after which the donated organs are frequently rejected by the receiver’s body because the cells are recognized as not being the person’s own. With stem cells generated from a person’s own somatic cells, rejection would not be an issue.
Because the extraction of stem cells destroys the embryo, people who feel that life begins with the very first division of a cell have ethical concerns about this type of research. Before this technology progresses, it will be important for society to define the rights of an embryo (if rights can be defined) and decide whether embryos can be manipulated for the treatment of other people.
Reproductive cloning is the process by which a nearly identical copy of an individual is created. In one sense, this type of cloning already occurs in the natural world. Although sexual reproduction of plants and animals involves the genetic information of two individuals combining to create a unique hybrid, asexual reproduction occurring in plants does not involve the combination of genetic information. In this case, an identical copy of the plant is naturally produced. Artificial reproductive cloning has enabled the cloning of animals as well. In this procedure, SCNT is used to create an embryo whose nuclear DNA is identical to that of another individual. This embryo is then cultivated until it is ready to be inserted into the womb of a surrogate parent. The embryo is gestated, and eventually a clone is born. The first mammal to be successfully cloned and raised to adulthood was Dolly, a sheep, in 1997.
Since Dolly, many other animals have been cloned, including goats, cows, mice, pigs, cats, horses, and rabbits. Nevertheless, the cloning of animals remains very difficult and inefficient; it may take over 100 tries to produce a single clone successfully. Previous attempts have also shown that clones have an unusually high number of health concerns, including compromised immune function and early death.
The inefficiency of current cloning technology, along with the compromised health of clones, raises further ethical concerns about the artificial creation of life and the manipulation of individuals for the benefit of others.
The American Medical Association (AMA) has issued a formal public statement advising against human reproductive cloning. The AMA maintains that this technology is inhumane because of both the inefficiency of the procedure and the health issues of clones. The President’s Council on Bioethics worries that cloning to produce children creates problems surrounding the nature of individual identity as well as the difference between natural and artificial conception.
Although some individuals and groups have claimed to have successfully cloned a human, these claims have not been substantiated. In the United States, federal funding for human cloning research is prohibited, and some states have banned both reproductive and therapeutic cloning.
- American Medical Association, Human Cloning, http://www.ama-assn.org/ama/pub/physician-resources/medical-science/genetics-molecular-medicine/related-policy-topics/stem-cell-research/human-cloning.page
- Fritz, Sandy, ed., Understanding Cloning. New York: Warner Books, 2002.
- Haugen, David M., et al., eds., The Ethics of Cloning. Detroit: Greenhaven Press, 2008.
- Klotzko, Arlene Judith, A Clone of Your Own? The Science and Ethics of Cloning. New York: Cambridge University Press, 2006.
- The Presidental Comission for the Study of Bioethical Issues, http://www.bioethics.gov/
- Shmaefsky, Brian, Biotechnology 101. Westport, CT: Greenwood Press, 2006.
- Wilmut, Ian, et al., “Viable Off spring Derived from Fetal and Adult Mammalian Cells.” Nature 385, no. 6619 (1997): 810–813.