Sir Ian and his team fused the genetic information from an adult sheep cell nucleus with an egg cell to form an embryo that developed into a genetically identical copy of the original adult.
The adult cell whose nucleus was transferred into the egg that became Dolly had a male imprinted genome that was inherited at birth and copied to every cell of the donor's body.
Reproductive cloning, which created Dolly the sheep in 1997, involves transferring the nucleus of an adult cell into an egg, giving the resulting embryo a full set of genes without the normal sperm-meets-egg fertilisation step.