clone

Exact replica – in genetics, any one of a group of genetically identical cells or organisms. An identical twin is a clone; so too are bacteria living in the same colony. ‘Clone’ also describes genetically engineered replicas of DNA sequences.

British scientists confirmed in February 1997 that they had cloned an adult sheep from a single cell to produce a lamb with the same genes as its mother. A cell was taken from the udder of the mother sheep, and its DNA combined with an unfertilized egg that had had its DNA removed. The fused cells were grown in a laboratory and then implanted into the uterus of a surrogate mother sheep. The resulting lamb, Dolly, came from an animal that was six years old. However, in 1999, Dolly was revealed not to be an exact clone – research showed her mitochondria to have come mainly from the egg cell rather than the udder cell. Dolly was put down at the early age of six in February 2003 when it was found that she had developed a progressive lung disease.

This was the first time cloning of a mammal had been achieved using cells other than reproductive cells. Such a breakthrough has ethical implications, as the same principle could be used with human cells and eggs. The news was met with international calls to prevent the cloning of humans. The UK, Spain, Germany, Canada, and Denmark already have laws against cloning humans, as do some individual states in the USA. France and Portugal also have very restrictive laws on cloning.

In 2003 scientists reported cloning a horse and a rat for the first time.