Human cloning is the creation of a genetically identical copy of a human being, human cell, or human tissue. The term is generally used to refer to artificial human cloning, although human clones in the form of identical twins are commonplace, with their cloning part of the natural process of reproduction.
Although genes influence behavior and cognition, "genetically identical" does not mean altogether identical; identical twins, despite being natural human clones with nearly identical DNA, are separate people, with separate experiences and personalities. The relationship between an "original" and a clone is rather like that between identical triplets raised apart; they share nearly all of the same DNA, but little of the same environment. A lively scientific debate on this topic occurred in the journal Nature in 1997.[1] Ultimately, the question of how similar an original and a clone would be boils down to how much of personality is determined by genetics, an area still under active scientific investigation. (See nature versus nurture and cloning.)
Techniques
There are no documented cases of successful human cloning. However, the most successful common cloning technique in non-human mammals is the process by which Dolly the sheep was produced. Dolly was one of 276 attempts. It is also the technique used by Advanced Cell Technology (ACT), the first company to successfully[2] clone early human embryos that stopped at the six cell stage. The process is as follows: an egg cell taken from a donor has its cytoplasm removed. Another cell with the genetic material to be cloned is fused with the original egg cell. In theory, this process, known as somatic cell nuclear transfer, could be applied to human beings.
ACT also reported its attempts to clone stem cell lines by parthenogenesis, where an unfertilized egg cell is induced to divide and grow as if it were fertilized, but only incomplete blastocysts resulted. Even if it were practical with mammals, this technique could work only with females. Discussion of human cloning generally assumes the use of somatic cell nuclear transfer, rather than parthenogenesis.
In January, 2008, Wood and Andrew French, Stemagen's chief scientific officer in California, announced that they successfully created the first 5 mature human embryos using DNA from adult skin cells, aiming to provide a less-controversial source of viable embryonic stem cells. Dr. Samuel Wood and a colleague donated skin cells, and DNA from those cells was transferred to human eggs. It is not clear if the embryos produced would have been capable of further development, but Dr. Wood stated that if that were possible, using the technology for reproductive cloning would be both unethical and illegal. The 5 cloned embryos, created in Stemagen Corporation lab, in La Jolla, were later destroyed.[3][4][5]
UK scientists clone human embryo
 There is controversy around human cloning |
British scientists say they have cloned the country's first human embryo. The Newcastle University team took eggs from 11 women, removed the genetic material and replaced it with DNA from embryonic stem cells.
The aim of this kind of work - the subject of fierce debate - is to make cloned embryos from which stem cells can be used to treat diseases.
Meanwhile South Korean scientists say they have created stem cells to match individuals for the first time.
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Stem cell lines were created by taking genetic material from the patient and putting it into a donated egg.
The resultant cells were a perfect match for the individual and could mean treatments for diseases like diabetes without problems of rejection.
Therapeutic cloning - believed to have huge potential to treat disease and disability - is allowed in Britain.
Reproductive cloning - the cloning of human embryos with the intention of creating a baby - was made illegal in 2001.
 |  We are talking about several years before we are talking about a cell-based therapy that can go back into the patient  |
The UN recently voted in favour of a ban on all human cloning, but this was non-binding which means the UK can continue to do therapeutic cloning.
The use of embryonic stem cells is controversial, with opponents arguing that all embryos, whether created in the lab or not, have the potential to go on to become a fully fledged human. Others fear there are safety concerns.
Supporters of cloning say it could offer numerous benefits in the future, such as fighting disease, battling infertility or preserving endangered species.
'Unsafe and inefficient'
 Dr Stojkovic: "There is a long way to go" |
Criticising the Newcastle research, Julia Millington from the ProLife Alliance said cloning for research purposes was profoundly unethical.
Josephine Quintavalle from CORE said: "No matter how it is created, a human embryo's destiny should be to live and not to be turned into human stem cells."
Life said cloning was "unsafe and inefficient", and involved exposing women to dangerous fertility drugs in order to collect sufficient eggs.
| STEM CELLS Stem cells are master cells, obtained from early-stage human embryos, with potential to develop into any of the body's tissue types There are different types, but scientists believe the most useful stem cells come from the tissue of embryos The copy pre-embryo created for therapeutic cloning is destroyed in the process |
In the Newcastle research, three of the resultant clones lived and grew in the laboratory for three days and one survived for five days.
The critical factor for success appeared to be how quickly the egg was collected and manipulated, Professor Alison Murdoch and colleagues found.
The clone that lasted for five days had been collected and manipulated within 15 minutes.
Other tissues
Stem cells have the ability to develop into virtually any tissue in the body and could, in theory, be used to replace damaged cells in conditions such as Parkinson's disease and diabetes.
| HAVE YOUR SAY Human cloning is essentially inevitable, and we would do well to embrace its great prospects Robert Yang, California, USA |
But Professor Murdoch said this was still a long way off.
"We are talking about several years before we are talking about a cell-based therapy that can go back into the patient," she said.
Colleague Dr Miodrag Stojkovic said: "I'm really happy but I know that this is just the beginning of a long journey so we have to continue to try to derive stem cells that will definitely help us one day to cure diseases."
The UK research is published in Reproductive and BioMedicine Online.
Cloning