Health Editor Barry Nelson answers some of the questions thrown up by the controversial issue of therapeutic cloning.

Q Why are scientists trying to clone human beings. Won't it lead to Frankenstein-style experiments or designer babies?

A Scientists in the UK and other parts of the world have stressed that their work is intended to lead to the development of new ways of treating patients with conditions such as Parkinson's disease and diabetes. While there are fears that some maverick scientists might be tempted to clone human babies, "official" scientists have ruled this out.

Q How are human embryos cloned? What did the Newcastle University scientists do?

A The work of the Newcastle team can be more accurately described as nuclear transfer. It involves removing the genetic material from a human egg cell and replacing it with the genetic material of an unrelated patient. This cell is then made to divide into stem cells - which have the potential to develop into almost every type of human cell, including heart, nerve and pancreatic cells.

Q Where do the Newcastle scientists get their human egg supply?

A The eggs - their technical name is oocytes - are voluntarily donated by women having fertility treatment. Because they produce large numbers of eggs, a small amount can be donated to research without reducing the woman's chances of conceiving.

Q Aren't the eggs potential human beings? Are the scientists committing a crime?

A The scientists would say that because the eggs are unfertilised they could not become fully developed human beings. The process of nuclear transfer also removes the original genetic material from the mother's side and replaces it with genetic material from an un-related patient.

Q How do scientists know that stem-cell therapy will work. Has it been tried out on humans?

A Researchers in the US have already cured a pig of heart disease using human embryonic stem cells and scientists have also seen benefits in rats and mice suffering from a form of Parkinson's disease.

Q Why is the work of the Korean scientists so significant?

A The Koreans have demonstrated that it is possible to use the new cloning techniques to create stem cells which are genetically tailored to match patients with particular diseases. It suggests stem cell therapy can become a reality in years to come. But it must be remembered the technique will not be able to treat conditions such as cancer and diseases caused by viruses, such as Aids.