clone

The production of a clone (an exact replica) happens naturally when a zygote undergoes division. This is the process that brings about multiple births such as identical twins and triplets. Zygote division can be induced in vitro with the resulting embryos then implanted into surrogate mothers. The offspring are all clones of each other but not of their parents.

The cloning of Dolly the sheep by the Roslin Institute in Edinburgh was a genetic milestone. It was the first successful clone produced using genetic material from an adult (udder) cell rather than from a gamete (egg or sperm). The DNA from the udder cell was fused with an ovum stripped of its own DNA. The fused cells divided in vitro to form an embryo that was then implanted into a surrogate mother. The resulting lamb was a clone of the ewe that had provided the udder cell.

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 had been achieved using cells other then reproductive cells. The cloning 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.

In July 2001, the US House of Representatives approved a comprehensive ban on human cloning, even for scientific research, and promised severe penalties for those caught flouting it. Although US president George W Bush announced in August that he would allow federal funds to be used for research on existing lines of embryonic stem cells, he said he would not allow any cloning to create new embryos.

Humans have been cloning plants for hundreds of years. Taking cuttings from a good fruit tree creates clones (see variety). All apple trees of the Bramley variety have been cloned from the original Bramley apple tree.

Cloning can also refer to the production of multiple copies of sections of DNA rather than the whole DNA complement of an organism. Cloning makes identical copies of a gene that can then be introduced into another organism to work for us. An example of this would be the cloning of the gene for human growth hormone. This gene can be introduced into bacteria so that the bacteria make the hormone. The hormone is extracted so that it can be used to treat people who do not produce enough of the hormone.

Cloning worldwide In June 1997, in response to the recommendations of the National Bioethics Advisory Commission, President Clinton proposed a five-year ban on cloning a human being. He said this would not stop the cloning of animals or of human DNA. The first binding international ban on human cloning was signed in January 1998 by 19 European countries. The text, which was an addition to the European Convention on Human Rights and Biomedicine, placed a total ban on human cloning although it allowed the cloning of cells for research purposes.

The UK did not sign the protocol because it was not yet a signatory to the convention. The protocol, agreed to by European leaders at a summit in October 1997, also did not include Germany, which claimed the measure was weaker than the German law already in place forbidding all research on human embryos. In mid-August 2000, the UK government approved the cloning of human embryos for medical purposes.

Human cloning From 1997, various scientific groups claimed to be developing human cloning. In December 2002, Clonaid, an organization founded by the Raelian Sect, announced the birth of the first human clone, but failed to produce any DNA evidence to back up their claim. In April 2003 the Italian doctor Severino Antinori announced that he was treating a woman who was pregnant with a cloned embryo, though this was later denied. In September 2003, Dr Panos Zavos claimed to have created the world's first human embryo and announced in January 2004 that he had successfully implanted this into a surrogate mother. In February 2004, South Korean scientists led by Woo Suk Hwang of Seoul National University reported that they had cloned 30 human embryos. Their aim was to grow the embryos to obtain embryonic stem cells from them; this procedure, if successful, removes some of the moral implications of destroying natural embryos to collect stem cells. In 2005 scientists developed a stem-cell line from cloned human cells for the first time. A team of researchers at Seoul National University, South Korea produced patient-specific embryonic stem-cell lines from human donors, some of whom were suffering from diseases such as diabetes.