How Things Work: Cloning
Science fiction has often portrayed settings in which a person runs into his or her clone. However, one creature far from fiction has actually been able to see a replica of itself. Dolly the sheep (named after country singer Dolly Parton), born on July 5, 1996, was the first mammal successfully cloned from an adult cell. Cloned by Ian Wilmut and his team at Scotland’s Roslin Institute, Dolly was even the mother to six lambs bred the old-fashioned way.
According to the National Human Genome Research Institute, cloning is the process by which an “exact genetic replica of another cell, tissue, or organism is created.” There are three types of artificial cloning: DNA cloning, reproductive cloning, and therapeutic cloning. As described on the website of the Human Genome Project, in DNA cloning, a DNA fragment from one organism is transferred to a self-replicating element such as the plasmid in bacteria.
Plasmids are rings of DNA found in bacteria and are not part of the bacterial chromosome. Plasmids are able to divide and replicate on their own. Thus, when the plasmid divides, the DNA of interest will divide, and copies of the desired DNA can be obtained.
Reproductive cloning is a technology used to generate an animal with the same DNA as another existing animal. Dolly was created using this method in a process called somatic cell nuclear transfer. In this process, scientists transfer genetic material from the nucleus of a donor adult cell to an egg cell whose nucleus has been removed. This new egg cell containing the other genetic material is induced to divide a couple of times to form an embryo. This embryo is then transferred to another female host’s uterus.
Therapeutic cloning, also known as embryo cloning, aims at creating an embryo from which stem cells can be harvested. Stem cells found in embryos are undifferentiated cells and have the potential of developing into any cell type. Because of this property, they can be used to study human development and treat illnesses.
Although cloning can be very useful, it does not come without risks. Most cloning, especially reproductive cloning, is expensive and inefficient, with a 90 percent rate of clones’ failure to produce viable offspring.
Many studies in Japan and Australia have shown that cloned animals that do not live long enough are good subjects to study how clones age.
In 2002, researchers at the Whitehead Institute for Biomedical Research in Cambridge, Mass., discovered that around 4 percent of the genes from cloned mice functioned abnormally due to changes in the normal activation or expression of certain genes.
However, despite all the setbacks from failed attempts, genetic cloning is still valuable because it aids humans in learning about technologies like gene therapy, which can be used to treat certain genetic diseases by introducing virus vectors that carry corrected copies of defective genes into the cells of a host.
Cloning can also use genes from different organisms to improve the nutritional value of genetically engineered food. Reproductive cloning could be used to repopulate endangered species.
Therapeutic cloning has the potential of producing a human organ from a single stem cell and can help replace damaged cells and organs in degenerative diseases like Alzheimer’s and Parkinson’s. In fact, many scientists hope that therapeutic cloning can one day be used for purposes like organ transplants.
In therapeutic cloning, DNA would first have to be extracted from the person who needs the transplant, and that genetic information will be inserted into an enucleated egg (one without a nucleus).
Soon after this new egg containing the patient’s DNA begins to divide, it will produce an embryo from which stem cells can be extracted. These embryonic stem cells can grow to be any tissue type and can be used to generate organs that are a genetic match to the recipient.
There has always been some controversy regarding whether humans should be cloned. Some believe that due to the lack of understanding about reproductive cloning, it is unethical to attempt to clone humans.
This is especially true if the statistics of premature death in cloned animals and other debilitating conditions (such as “large-offspring syndrome”) are considered.
The American Medical Association recognizes that animal cloning has produced some very significant outcomes in the field of science, but because people do not fully understand the risks and results of cloning, it, along with the National Bioethic Advisory Commission, supported the halt in federal funds toward human cloning in 1997.
Also, many ethical debates have surrounded the subject of human embryonic stem cell research. In 2001, former U.S. President George W. Bush announced his decision to ban federal funding for research using stem cell for lines created after that date. However, as reported on CBS News, on March 9, 2009, President Barack Obama said he was allowing federal taxpayer dollars to fund significantly broader research on embryonic stem cells because “medical miracles do not happen simply by accident.” This action gives researchers new hope for the future of stem cell research and, subsequently, cloning. However Obama has publicly stated that he will never allow the use of cloning for human reproduction.