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.
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.