For the second time, the Human Fertilisation and Embryology Authority has given the go-ahead for a team of British scientists to clone human embryos.
Cloning could tackle disease
BBC News Online examines the implications of the case.
What are the scientists hoping to do?
Professor Ian Wilmut and a team at Kings College in London will clone early stage embryos to study a condition called motor neurone disease (MND).
What is MND?
MND is caused by the death of cells - called motor neurones - that control movement in the brain and spinal cord.
It affects about 5,000 people in the UK. Half of people with MND die within 14 months of diagnosis.
Weakness in the muscles that supply the face and throat also cause problems with speech and difficulty chewing and swallowing.
What will the research involve?
The team are investigating a cloning technique called cell nuclear replacement (CNR), in which the nucleus of a human egg cell is removed and replaced with the nucleus from a human body cell, such as a skin cell.
The replacement nucleus will come from patients with MND so the embryo also has MND.
The egg would then be stimulated to develop into an embryo.
The embryo would be allowed to develop for around six days, until it was at the blastocyst stage, before being destroyed.
What is the point of the research?
By cloning cells from MND patients, the researchers will be able to see how the illness develops in an embryo.
They would remove cells from the embryo while it was still in the earliest stages of development, before destroying it.
How is this different from earlier cloning research?
Up until now, scientists have wanted to create cloned embryos to see if they can be grown into tissues to repair damaged body parts.
Experts at the University of Newcastle, who were the first to be given the go-ahead by the HFEA, have been investigating new treatments for conditions including diabetes, Parkinson's and Alzheimer's disease.
Could it be done a different way?
Cloning opponents have said scientists should look for alternative ways to investigate MND, such as studying embryos that have been rejected from IVF use because they carry an inherited disease.
But Professor Peter Braude, from the Centre for Preimplantation Genetic Diagnosis at King's College, London, said: "Unlike other genetic disorders like cystic fibrosis and Huntington's disease, for which stem cell lines have already been created from affected embryos following preimplantation genetic diagnosis, there is no other way of producing a motor neurone stem cell line other than using cloning techniques."
Is it legal?
Yes. The Human Fertilisation and Embryology Authority decided to make "therapeutic" cloning legal in 2001.
This means that scientists can apply for a licence to clone human embryos provided they intend to use them to study disease in a laboratory situation only.
The cloning of human embryos with the intention of creating a baby - reproductive cloning - is still strictly banned in the UK.
Embryos used for research must be destroyed when the work is finished. At this stage, they are still in an early stage of development, a bundle of several hundred cells.
It is controversial?
Yes. Opponents say an embryo, regardless of its stage of development, is still potentially a human being in the making.
Others question the potential benefits of the work.
A spokesman from Comment on Reproductive Ethics (CORE) said: "Human cloning remains dangerous, undesirable and unnecessary."
But proponents argue that experimentation takes place long before an embryo begins to develop any nervous system, or sense of self - and as such cannot be defined as a human life.
They argue that the work is vital if effective treatments are to be found for debilitating diseases.
Have other scientists created cloned human embryos?
Yes. A South Korean team announced earlier this year that they had 30 embryos that were the exact genetic copies of the women who donated the eggs and cells to make them.
The embryos were allowed to develop for several days, and embryonic stem cells were extracted from them.
The eventual aim, in this case, is to use such cells to replace those that have failed in patients with degenerative diseases, such as some heart conditions and Parkinson's, or in spinal cord injuries.