In 1997 photographs of a sheep called Dolly appeared on the front page of newspaper around the world. She looked quite ordinary, but Dolly was different from other sheep. She was an identical copy of another adult sheep. In other words, she was a clone. Before Dolly, scientists had only been able to clone large animals using cells taken from embryos. They had tried to do it using cells from adult animals, but it hadn't worked until now. That's why Dolly was so special.