Dolly the Sheep Is Cloned from an Adult Cell

On 5 July 1996, a female Finn-Dorset lamb was born at the Roslin Institute near Edinburgh, marking a fundamental turning point in reproductive biology. Named Dolly, she was the first mammal ever cloned from an adult somatic cell rather than from an embryonic cell. The project was led by Keith Campbell, Ian Wilmut, and their colleagues at the institute, in partnership with the biotechnology company PPL Therapeutics and with financial backing from the United Kingdom Ministry of Agriculture. Her birth challenged the prevailing scientific belief that once body cells had matured into specialized tissue, their developmental fate became irreversible.

Although previous experiments had produced animal clones, earlier successes had depended on early-stage embryonic tissue or amphibians, such as the African clawed frogs cloned by John Gurdon in 1958. Dolly, by contrast, originated through somatic cell nuclear transfer using a differentiated mammary cell taken from a six-year-old adult ewe. In this procedure, scientists removed the nucleus from an unfertilized sheep egg and replaced it with the nucleus of the adult cell. An electric shock stimulated this reconstructed cell to begin dividing, and once it developed into a blastocyst, researchers transferred the embryo into a surrogate mother. Dolly thus had three maternal contributors: one sheep provided the egg, another supplied the donor DNA, and a third carried her to term.