Dolly the sheep may have been the world's most famous clone, but she was not the first. Cloning creates a genetically identical copy of an animal or plant. Many animals - including frogs, mice, and cows - had been cloned before Dolly. Plants are often cloned – taking a cutting produces a clone of the original plant. Human identical twins are also clones.

Dolly was the first mammal to be cloned from an adult cell, rather than an embryo. This was a major scientific achievement, but also raised ethical concerns.

Since 1996, when Dolly was born, other sheep have been cloned from adult cells, as have mice, rabbits, horses and donkeys, pigs, goats and cattle. In 2004 a mouse was cloned using a nucleus from an olfactory neuron, showing that the donor nucleus can come from a tissue of the body that does not normally divide.