Do you remember Dolly the sheep? Dolly birth made history in 1996 because she was genetically identical to her mother who had been born six years earlier. The excitement over this birth, when the news was finally announced in February 1997, was because she was the first mammal to be cloned artificially in a laboratory from an adult cell rather than an embryo. Before Dolly, cloning was the stuff of science fiction and her birth was heralded as a major scientific breakthrough achieved by a team led by Dr Ian Wilmut, an embryologist, at the Roslin Institute, Edinburgh, Scotland.
Cloning is the creating of a genetically identical copy of an individual. Cloning occurs naturally. Identical twins are natural clones and cloning is a method used by many micro-organisms, single cell animals and plants in order to reproduce and increase their numbers. Bacteria, amoebae, yeast and hydras all survive because of natural cloning. In horticulture cloning has been commonplace since ancient times and many varieties of plants are cloned simply by obtaining cuttings of their leaves, stems or roots and replanting them. Gardeners call this process vegetative reproduction or taking cuttings. It was the British biologist J. B. S. Haldane speaking at a convention in 1963 who first coined the term clone which is the Greek word for twig. Prior to that artificial cloning had been called nuclear transfer.
There are two main methods of animal cloning:
1. Embryo Cloning So far most animal clones have been produced using this method. The embryos produced are not identical to either parent, as there is a mix of genes from both parents.
2. Nuclear Transfer This was the method used to clone Dolly the sheep. It produces a clone identical to its parents
Like many major scientific achievements the earlier work done by scientists provided the foundation for others. Towards the end of the nineteenth century an improvement in lenses meant that scientists began to be study embryology using microscopes and consequently the science began to develop. In 1938 Hans Spemann a Nobel Prize winner experimented by artificially cloning salamanders. In his description he referred to the process as 'nuclear transportation'. The 1950s saw more experiments carried out, this time by Robert Briggs and Tom King. But it was John Gurdon who cloned frogs and newts by removing the nucleus from an egg and replacing it with a nucleus taken from a cell of a tadpole. This method was called nuclear transfer. Although successful in experiments with frogs and tadpoles Gurdon was unsuccessful in cloning a cell taken from an adult frog or toad, and despite hundreds of laboratory experiments in the 1970s and 1980s scientists failed to clone cells taken from mammals.
Success eventually came to the Roslin Institute in 1995 when two sheep, who were subsequently named Megan and Morag, were cloned from embryo derived cells that had been cultured in the laboratory. And then in 1996 Dolly was born, the only full term pregnancy out of 29 embryos which in turn developed from 277 cell fusions. Dolly was the first mammal to be born by the nuclear transfer method. At first Dolly was a "Sclone alone". Since her birth scientists in different parts of the world have reported the cloning of sheep, cattle, pigs, goats and mice, although success has eluded them so far in cats, dogs, rabbits and monkeys.
Scientists believe that the benefits of cloning might be found in several areas:
The Manufacture of Drugs
Many drugs are extremely expensive, not to say difficult to produce and because of this their use has often to be rationed. Scientists hope that by cloning animals it will help their research aimed at producing medicines in the milk of these mammals. Cloned animals would also help in the fight against cancers by producing antibodies that would fight such diseases.
An improvement in farming stock
Animals could be recreated that have useful characteristics such as cows with a high milk yield, chickens that could lay lots of eggs and beef cattle that produce particularly high quality meat.
It is already possible to produce new skin from cloned cells to treat people suffering from horrific burns. Scientists hope that cloning will also help transplant patients by:
- enabling animals to be bred specifically for organ donation
- helping to build new hearts, kidneys, livers etc in the laboratory.
- the use of stem cells to treat degenerative diseases.
The Ethical Concerns of Cloning
In the 1950s and 1960s the general public viewed experiments with genetics as beneficial to mankind. Cloning offered the possibility of real scientific advances that could improve lives and save them. Today most of the concerns about cloning relate to the possibilities of cloning human beings either for tissue replacement or as designer babies.
In the USA the National Bioethics Commission and Congress are examining the issues that surround cloning and in the UK the Human Embryology and Fertilisation Authority, the House of Commons Science and Technology Committee, the Human Genetics Advisory Commission and the Council of Europe have all recommended that human reproductive cloning should be banned; although therapeutic cloning for tissue engineering has found to be less objectionable, and in 2004 a licence was granted to clone human embryos in the hope of finding a cure for major diseases. This, however, will have to be carefully regulated. Dr Wilmut who cloned Dolly the sheep has himself spoken out against human cloning. Suggestions of a Brave New World of cloned super humans have been dismissed.
Attention has also focused on the use of cloning as a means of saving endangered species of animals, although this has not attracted very many objections. It would be a different matter, however, if extinct animals were recreated in a laboratory (where have we heard of this!?).
Dolly lived a rather pampered existence at the Roslin Institute as befitted the most famous sheep in the world. She mated and produced an offspring, Bonnie, in the normal way, thus showing that this was possible with cloned animals. And in most other ways Dolly was the same as any other sheep of her chronological age, except that she had the DNA of a six year old ewe. In 2002, however, Dolly was found to be suffering from arthritis in one of her hind leg joints and this premature ageing was questioned. She then developed lung problems and in July 2003 Dolly was euthanased.
Although in most ways she was the same as other sheep of her chronological age Dolly only survived half her expected life span. Scientists reported that her premature death was triggered by a virus caught from a sheep who had died two years earlier and it was not specifically related to the process of cloning, but it raised the question of the wisdom of cloning. There has been no further attempts to clone another Dolly.