The creation of Dolly the sheep, the first mammal to be cloned successfully from an adult cell, was announced to the world on this day in 1997.
Dolly, a Finn Dorset sheep, was born on July 5 the previous year at the Roslin Institute near Edinburgh. She came about after scientists extracted the nucleus of a cell from the udder of a six-year-old ewe and transplanted it into an egg cell from a second sheep.
The egg was then inserted into the uterus of a third sheep, to develop. The last surrogate, a Scottish blackface ewe, produced Dolly - a genetic duplicate of the animal that donated the original udder cell.
It was later revealed that Roslin scientists made a total of 277 attempts to clone a sheep from an adult cell, and Dolly was their only success.
Embryologist Dr Ian Wilmut, who along with Dr Keith Campbell and other colleagues was responsible for the successful cloning, said that the research would enable the study of genetic diseases for which there was currently no cure. The use of cloning has also been touted as a possible weapon in the fight to preserve endangered species.
Dolly’s creation was, however, considered controversial by animal rights campaigners, as well as religious groups who questioned the ethics of the work amid fears that it was the first step on the road to the cloning of human beings.
Dolly was put down at the age of six in 2003 after developing lung disease. Her preserved remains are now on display at the National Museum of Scotland.
[April 25, 1953: Crick and Watson crack the code of life as paper reveals structure of DNA]
[February 19, 2001: Foot-and-mouth outbreak declared in UK]
Dolly the sheep - Did you know?
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Dolly was by no means the first mammal to be cloned - scientists had cloned plants, amphibians, sheep and even cows previously using embryonic cells – but she was the first to be successfully cloned from the cell of an adult.
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Ian Wilmut would explain that it was because the process had started with a mammary gland cell from a ewe that the clone was named Dolly - calling it “our affectionate tribute to the buxom American singer Dolly Parton”.
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She would become the subject of global fascination and debate, being featured on the cover of Time Magazine, while US President Bill Clinton asked experts to review the implications of her birth.
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Dolly would spend her entire life at the Roslin Institute under the watchful eye of scientists, even sleeping indoors due to security concerns.
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She was mated with a Welsh Mountain ram named David, and produced six lambs of her own over three years. They were named Bonnie, Sally, Rosie, Lucy, Darcy and Cotton.
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The average sheep lives around 12 years so some commentators blamed the cloning process for Dolly’s early death. Subsequent research has found that since the donor cells came from a sheep of six years of age, Dolly's DNA was "older" than that of a newborn lamb.
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A post mortem revealed that Dolly died from a form of lung cancer that is fairly common in sheep – particularly in those kept indoors, as it is passed on by droplets in the breath.
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Subsequently nuclear transfer has been used to clone pigs, deer, horses and bulls. A Pyrenean ibex – officially extinct since 2000 – was cloned from frozen tissue in 2009, although it died shortly after birth due to a lung defect.
