The first cloned mammal was made from a single adult cell

In 1996, Ian Wilmut's team at the Roslin Institute created Dolly the sheep by transferring the nucleus of an adult mammary-gland cell into an egg with its own DNA removed. She was the first mammal ever cloned from a fully specialized adult cell rather than an embryo. Dolly proved a mature cell still carries the complete genetic instructions to build an entire animal.

— Ian Wilmut et al., Dolly (sheep) — Nature, 27 February 1997