2. Dolly the sheep became a scientific sensation when her birth was announced in 1997. Her relatively early death in February 2003 fuels the debate about the ethics of cloning research and the long-term health of clones. What is it about Dolly that is so special? How was she created? And did she die young because she was a clone? Dolly the sheep (1996-2003)

3. Exactly how 'adult' DNA is reprogrammed is a mystery. At the Roslin Institute, scientists replaced the nucleus of the egg cell with the nucleus from the parent cell - in Dolly's case, an udder cell. Somehow, the egg cell reprogrammed the donated DNA contained within its new nucleus, and Dolly was the result. How Dolly was created? (I) Reproduction diagram

4. The manipulation was done using microscopic needles, a method pioneered in human fertility treatments in the 1970s. The resulting embryo was implanted into the womb of a third, surrogate sheep. Dolly was born on 5 July 1996, and her birth was announced in early 1997. How Dolly was created? (II)

5. At 15.30 on Friday 14 February 2003, scientists at the Roslin Institute, Edinburgh, decided that Dolly, the world's most famous sheep, should be put down. She had been suffering from a progressive lung disease. Dolly's death, like her birth, is bound to raise fresh fears about the wisdom of cloning. Goodbye, Dolly Dollys graveyard

6. . An early death? At only 6 years old, Dolly was relatively young when she died. But there's no proof that cloning was to blame. Sheep can live to 11 or 12 years of age, and lung infections are common in older sheep, particularly those housed indoors. There is no evidence that cloning was a factor in Dolly contracting the disease. Dr. Harry Griffin, Acting Director, Roslin Institute

7. Because Dolly's genetic material came from a 6-year-old sheep, questions have always been asked about her "true" age. In 1999, some of the scientists who created Dolly studied her genetics. They found that structures in her cells were slightly shorter than would be expected in a sheep of her age conceived naturally - so in a way Dolly's DNA was 'older' than her body. Scientists realized then that Dolly might die young. Old before her time?

8. A postmortem examination confirmed the cause of Dolly's lung problems as sheep pulmonary adenomatosis (SPA), a lung tumor brought on by a virus. The examination also confirmed what vets had suspected since early 2002 - that she had arthritis in her hind legs. Until the first signs of arthritis were detected, Dolly had shown no signs of ill health and had given birth to four healthy lambs. No other abnormalities were uncovered by the postmortem. There's no proof that Dolly died young because she was a clone, but scientists still have many questions about cloning. Cause of death

9. Ian Wilmut, who led the team that cloned Dolly, has always spoken out against human cloning. It took hundreds of attempts to produce Dolly and, even now, the cloning process is far from perfect. Dolly's arthritis and now relatively young death fuel concerns that even clones appearing healthy at birth may have underlying genetic abnormalities. But after all, she's only one sheep, and the results of her postmortem haven't given us concrete answers about the safety of cloning. The handful of experts who advocate human cloning are unlikely to be deterred. Dolly and human cloning

10. Dolly was quite young when she died. But she died from a condition that is fairly common in sheep of her age. What do you think her death means for the future of cloning? Cloning may lead to many important scientific breakthroughs and medical treatments, but is it ethical? Should animal cloning experiments continue? Should human cloning experiments be allowed? What do you think?