written by: Rafael•edited by: Paul Arnold•updated: 9/4/2009
The process of cloning is a controversial and emotive research enterprise, but one that has practical applications in agriculture, genetics, and medicine. Find out more about human and animal cloning, reproductive cloning and how cloning is done in our FAQ.
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Cloning is a general term used to describe a process of exact duplication. It really came into the general public's consciousness with the creation of Dolly the Sheep. Since then many other animals have been cloned, and the technologies involved have applications in agriculture, genetics, and medicine.
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What is DNA Cloning?
There are different types of cloning, and DNA cloning is one of them. Gene and molecular cloning also refer to this type of cloning. In DNA cloning a specific fragment of DNA (a gene or group of genes) is duplicated over and over. This is done by transferring the DNA fragment of interest into aself-replicating organism (generally a bacterium) to replicate the fragment.
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What is Reproductive Cloning?
This is perhaps the most widely known process of cloning known since the highly publicized Dolly the sheep. Reproductive cloning is the creation of an animal that is an exact duplicate copy of the nuclear DNA of its donor. The technology involved is called “somatic cell nuclear transfer" (SCNT)."In this SCNT technology DNA from the nucleus of a donor adult cell is transferred to an egg cell that has had its own nucleus extracted. If the new egg cell becomes viable it will develop and grow into an individual with the characteristics of the donor’s cell. This is how Dolly the sheep and other animals have been cloned.
The technology is notoriously inefficient, with many embryos having to be created just to get one or two viable offspring.
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What is Therapeutic Cloning?
Basically, therapeutic cloning is the use of cloning for therapeutic purposes. Therapeutic cloning involves the development of human embryos. The objective here is not to clone a human being but to use cloned embryos for research and therapeutic purposes.
Once the nuclear transfer has taken place and the egg becomes viable it develops. After 5 days a blastocyst is formed. Blastocysts contain in its inner structure stem cells. Stem cell harvesting is the ultimate purpose of therapeutic cloning. Stem cells can be used to generate virtually any type of specialized cell in the human body.
This type of cloning raises some serious ethical issues (for example, blastocysts need to be destroyed for harvesting stem cells). The first human embryos for the purpose of advancing therapeutic research were created in 1991 by Advanced Cell Technologies (ACT), a biotech company. More recently, in 2008, it was reported that 5 human viable embryos had been created (and later destroyed) from skin cells in Stemagen Corporation lab.
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Can Organs be Cloned?
Human organs for transplant are always difficult to obtain. Because of the theoretical possibility of cloning human cells and organs many researchers and scientists believe in the possibility of cloning human organs for transplant purposes. However, there are many scientific and technical obstacles to overcome, in addition to the ethical and religious questioning of such practices.
One way to produce cloned organs would be to use stem cells and “stimulate" them to direct their development into specific tissue cells (heart, skin, kidney, etc). This strategy is far from being successful at the moment. But recently researchers were able to use stem cells to form adult human skin cells. They did it by regulating certain genes that influence cell differentiation. The process is plagued with uncertainty and lack of knowledge.
Another strategy to obtain cloned organs for transplantation would be to use animals to “produce" organs needed by humans. A major issue here would be the possibility of organ rejection by humans. Genetically modified pigs would be an excellent candidate for this strategy. Genetically speaking they are quite similar to humans, although issues with organ rejection still need to be resolved. The genes that cause the immune reaction would have to be silenced.