Q&A: What is cloning?

This calf clone died young, demonstrating the primitive state of current technology

Cloning is the most high profile of the new biotechnologies and the one which causes the most heated debate over its worth. BBC News Online answers the most common questions about cloning.

What is cloning?
Cloning is the creation of cells or whole animals using DNA from a single "parent", bypassing the normal reproductive process. The clone has identical DNA to the parent.

Is cloning unnatural?
No. Clones are frequently produced by natural means in the shape of identical twins.

How are clones created?
The most common process takes DNA from one cell and puts in a "hollowed out" egg. Chemicals and electricity are then used to encourage the new DNA to fuse with the egg and develop into an embryo. This technique is called nuclear transfer.

Why was Dolly important?
The sheep was the first mammal to be cloned using DNA taken from an adult cell. Previously, animals had only been cloned using embryo cells, which already have the potential to become a complete embryo in their own right. The big breakthrough with Dolly was to make a clone from an ordinary, adult cell - in this case from the udder of a ewe.

Are clones normal, healthy animals?

Goats, as well as sheep, cows and mice have been cloned

Dolly is, but scientist do not yet know whether this is the exception or the rule. Some initial evidence suggests that clones may have health problems and that they may age prematurely.

Could a human clone be born soon?
In theory, yes. The techniques used to create Dolly could be applied to humans. But the technology of reproductive cloning is still in its very early stages and there is much scientists do not understand. It took more than 200 attempts to make Dolly. The other embryos failed to implant in the surrogate mother or were miscarried. Even if a clone makes it to birth, it currently has a very low chance of surviving into adult life.

Has anyone said they will make live human clones?
A number of people have, including Chicago physicist Dr Richard Seed. However, few experts believe that these people have the skills to succeed.

Are there any benefits from cloning?
Yes. The techniques used have already demonstrated benefits. Polly, another sheep clone at the Roslin Institute in Edinburgh has had a human gene inserted so that it produces a blood-clotting agent needed by haemophiliacs in its milk. Cloning of human cells in a laboratory could yield perfectly matched tissue for surgical or genetic repair of humans.

Where does the law stand on live human clones?
In the UK, human cloning is already banned by law. President Bill Clinton has proposed banning research into producing human clones in the US for five years. There are also moves to establish international agreements banning live human clones.