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.
The prize is in stark contrast to Prof Gurdon's first foray into science when his biology teacher described his scientific ambitions as "a waste of time".
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 needed 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 transferring 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.
"The discoveries of Gurdon and Yamanaka have shown that specialized cells can turn back the developmental clock under certain circumstances.
"These discoveries have also provided new tools for scientists around the world and led to remarkable progress in many areas of medicine."
Prof Yamanaka said it was a "tremendous honour" to be given the award. He also praised Prof Gurdon: "I am able to receive this award because of John Gurdon.
"This field has a very long history, starting with John Gurdon."
It is hoped the techniques will revolutionise medicine by using a sample of person's skin to create stem cells.
The idea is that they could be used to repair the heart after a heart attack or reverse the progress of Alzheimer's disease.
Prof Gurdon, now at the Gurdon Institute at Cambridge University, said: "I am immensely honoured to be awarded this spectacular recognition, and delighted to be due to receive it with Shinya Yamanaka, whose work has brought the whole field within the realistic expectation of therapeutic benefits.
"I am of course most enormously grateful to those colleagues who have worked with me, at various times over the last half century.
"It is particularly pleasing to see how purely basic research, originally aimed at testing the genetic identity of different cell types in the body, has turned out to have clear human health prospects."
Prof Yamanaka, who started his career as a surgeon, said: "My goal, all my life, is to bring this stem cell technology to the bedside, to patients, to clinic."
The president of the Royal Society, Sir Paul Nurse, said: "I was delighted to learn that John Gurdon shares this year's Nobel prize for physiology or medicine with Shinya Yamanaka.
"John's work has changed the way we understand how cells in the body become specialised, paving the way for important developments in the diagnosis and treatment of disease.
"My congratulations go out to both John and Shinya."
Prof Anthony Hollander, the head of cellular and molecular medicine at the University of Bristol, said: "This joint Nobel Prize traces and celebrates the wonderful scientific journey from John Gurdon's pioneering early work to the sensational discovery of somatic cell reprogramming by Shinya Yamanaka.
"It's fantastic news for stem cell research."
Sir Mark Walport, the director of the Wellcome Trust, said: "John Gurdon's life has been spent in biology, from collecting insects as a child to over 50 years at the laboratory bench. He and Shinya Yamanaka have demonstrated conclusively that it is possible to turn back the clock on adult cells, to create all the specialised cell types in the body.
"Their work has created the field of regenerative medicine, which has the potential to transform the lives of patients with conditions such as Parkinson's, stroke and diabetes.
"This is a wonderfully well-deserved Nobel Prize."