Picture of identical twin boysIdentical twins are natural clones.

What is cloning?

Cloning is often found in nature: genes, cells, and plants all clone themselves. Identical twins are an example of a naturally-occurring clone.

Making a clone in the laboratory is more difficult.

How to artificially make a clone:

You need to combine an egg and an adult body cell, say a skin cell.

Remove the genetic material of the egg, so that it becomes an empty shell.

Extract the DNA from the skin cell and put this DNA into the egg.

Give the egg an electric shock to stimulate this DNA to reprogramme. This turns it back into a form of DNA that can grow into any cell type and develop into an embryo.

The original adult cell can then develop into an embryo.

This method is called Somatic Cell Nuclear Transfer or SCNT.

There are two types of cloning: therapeutic cloning and reproductive cloning. The first stage of both is the same and uses SCNT.

In reproductive cloning, the embryo is implanted in a uterus where it may grow into a whole organism. This has been carried out with animal embryos. The most famous cloned animal is ‘Dolly’ the sheep. Most attempts at reproductive cloning have been unsuccessful.

In therapeutic cloning, the embryo is not placed in the uterus. After five days of growth, stem cells are retrieved from the embryo. The embryo does not develop into a complete organism but its cells are grown in the lab.