Two pioneers of stem cell research have shared the Nobel prize for medicine or physiology.
John Gurdon from the UK and Shinya Yamanaka from Japan were awarded the prize for changing adult cells into stem cells, which can become any other type of cell in the body.
Prof Gurdon used a gut sample to clone frogs and Prof Yamanaka altered genes to reprogramme cells.
The Nobel committee said they had "revolutionised" science.
When a sperm fertilises an egg there is just one type of cell. It multiplies and some of the resulting cells become specialised to create all the tissues of the body including nerve and bone and skin.
It had been though to be a one-way process - once a cell had become specialised it could not change its fate.
In 1962, John Gurdon showed that the genetic information inside a cell taken from the intestines of a frog contained all the information need to create a whole new frog. He took the genetic information and placed it inside a frog egg. The resulting clone developed into a normal tadpole.
The technique would eventually give rise to Dolly the sheep, the first cloned mammal.
Forty years later Shinya Yamanaka used a different approach. Rather than transfering the genetic information into an egg, he reset it.
He added four genes to skin cells which transformed them into stem cells, which in turn could become specialised cells.
The Nobel committee said the discovery had "revolutionized our understanding of how cells and organisms develop".
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