Scientists led by Ian Wilmut and Keith Campbell fused the nucleus of a mammary-gland cell with an egg cell whose own nucleus had been removed, then implanted the embryo in a surrogate mother. Dolly was the only lamb from 277 attempts. Her birth was kept secret until February 1997, when it caused a worldwide sensation and debate over human cloning. She was named after the singer Dolly Parton, because the donor cell came from a mammary gland. She lived six and a half years.
Biologists had long believed that once a cell had specialised, becoming skin or liver or udder, its genetic program could not be reset. Frogs had been cloned from embryonic and tadpole cells, but no one had cloned a mammal from an adult cell. The Roslin team, supported by the biotechnology company PPL Therapeutics, was working toward sheep that would produce useful proteins in their milk.
The key was a technique of starving the donor cells of nutrients so that they entered a resting state before the nucleus was transferred. Out of 277 reconstructed eggs, 29 developed into embryos, and only one lamb was born, on July 5, 1996. Dolly had a white face, like the Finn-Dorset donor, while her surrogate mother was a Scottish Blackface.
When the result was published in Nature in February 1997, politicians around the world called for bans on human cloning. Dolly gave birth to six lambs of her own. She developed arthritis and a lung tumor caused by a virus and was put down in February 2003. Her stuffed body is displayed at the National Museum of Scotland.
Key people: Ian Wilmut, Keith Campbell