Fusion cell cloning
Fusion cell cloning involves replacing the nucleus of an unfertilised egg with the nucleus from a different cell. The replacement nucleus can come from an embryo, but if it comes from an adult cell, it is called adult cell cloning.
Dolly the sheep was the first mammal to be cloned using adult cell cloning. She was born in the UK in 1996 and died in 2003. Here's how she was produced:
An egg cell was removed from the ovary of an adult female sheep, and its nucleus removed.
The nucleus from an udder cell of a donor sheep was inserted into the empty egg cell.
The fused cell then began to develop normally, using genetic information from the donated DNA.
Before the dividing cells became specialised, the embryo was implanted into the uterus of a foster mother sheep. The result was Dolly, genetically identical to the donor sheep.