What is cloning?

It involves creating an embryo that is genetically almost identical to an existing person

How is it done?

Using a process known as cell nuclear transfer, the technique used to create Dolly the Sheep. The nucleus, containing most of a person’s DNA, is removed from an adult cell. This is then injected into an egg which has had its own nucleus removed. The resulting embryo is tricked into dividing using electricity and chemicals.

What can a cloned embryo be used for?

There are two possible applications. Scientists are interested chiefly in "therapeutic cloning" - creating cloned cells that may be useful for studying and treating disease. "Reproductive cloning" is more controversial - the creation of a cloned human being.

What is therapeutic cloning?

The idea is to produce a cloned embryo that is genetically similar to a patient, perhaps with a disease such as diabetes. This can then be used to extract embryonic stem cells that have the same DNA as that patient.

What is an embryonic stem cell?

These are master cells found in early-stage human embryos, which can form any tissue in the body.

Why are they useful?

In the short term, embryonic stem cells that carry the genes of a patient will be valuable for studying the progression of his or her disease, and for investigating new treatments. In the longer term, scientists hope to use cloned embryonic stem cells to create replacement tissue, which could be transplanted back into the patient to cure disease. As the cells would have the same DNA as the recipient, there would be no risk of rejection by the body’s immune system.

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