The February 1997 announcement that a sheep named Dolly had been born from a cloned adult mammary cell touched off a fierce scientific debate about the ethics of cloning. While frogs had been cloned from tadpoles since 1952, mice from embryos since 1970, and sheep and cattle from embryos since 1979, never before had a mammal been cloned from a somatic cell.

To create Dolly, Ian Wilmut, Keith Campbell, and their colleagues at the Roslin Institute in Scotland used a process called nuclear transfer. They removed the nucleus from a mammary cell and placed it into an egg cell which had had its DNA removed. After starving the egg cell of nutrients, the nucleus and donor cell were fused with an electrical charge and the egg was implanted into a surrogate sheep. Most scientists considered Dolly’s birth a giant breakthrough in biomedical research.

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