The Life of Dolly
The history of Dolly the sheep, from birth to death.
Dolly was born as part of a series of experiments at the Roslin Institute, when a better method of producing genetically modified livestock was being developed. If successful, this would mean fewer animals would need to be used in future experiments.
Scientists at Roslin also wanted to learn more about how cells change during development and whether a specialised cell, such as a skin or brain cell, could be used to make a whole new animal.
These experiments were carried out at the Roslin Institute and PPL Therapeutics by a team led by Professor Sir Ian Wilmut. Due to the nature of the research, the team was made up of people with a range of skillsets, including scientists, embryologists, surgeons, vets and farm staff.
Dolly was cloned from a cell taken from the mammary gland of a six-year-old Finn Dorset sheep and an egg cell taken from a Scottish Blackface sheep. She was born to her Scottish Blackface surrogate mother on 5 July 1996.
Dolly’s white face was one of the first signs that she was a clone because if she had been genetically related to her surrogate mother, she would have had a black face.
Dolly was named after the country music singer Dolly Parton.
Why was Dolly so important?
Dolly was the first mammal to be cloned from an adult cell. Her birth proved that specialised cells could be used to create an exact copy of the animal they came from.
This knowledge changed what scientists thought was possible and opened up a lot of possibilities in biology and medicine, including the development of personalised stem cells, known as iPS cells.
However, Dolly was not the first ever cloned mammal. That honour belongs to another sheep which was cloned from an embryo cell and born in 1984 in Cambridge, UK.
Two other sheep, Megan and Morag, had also been cloned from embryonic cells grown in the lab at the Roslin Institute in 1995 and a further six sheep, cloned from embryonic and foetal cells, were born at Roslin at the same time as Dolly.
What made Dolly so special was that she had been made from an adult cell, which no-one at the time thought was possible.
Dolly was announced to the world on 22 February 1997, to a frenzy of media attention.
The Roslin team chose to make the announcement at this time to coincide with the publication of the scientific paper which describes the experiments that produced her.
Dolly captured the public’s imagination – no small feat for a sheep – and sparked a public debate about the possible benefits and dangers of cloning.
In the week following the announcement, the Roslin Institute received 3,000 phone calls from around the world.
When Dolly was a year old, analysis of her DNA showed that her telomeres - caps on the ends of DNA molecules that protect them from damage - were shorter than would be expected for a normal sheep of the same age.
As an animal or person ages, their telomeres become progressively shorter, exposing the DNA to more damage.
It was thought that, because Dolly's DNA came from an adult sheep, her telomeres had not been fully renewed during her development. This could have meant that Dolly was biologically older than her actual age.
However, extensive health screens on Dolly at the time did not find any conditions which could be directly related to premature or accelerated ageing.
Dolly spent her life at the Roslin Institute and, apart from the occasional media appearance, led a normal existence with the other sheep at the Institute.
Over the years, Dolly had a total of six lambs with a Welsh Mountain ram called David. Their first lamb, Bonnie, was born in April 1998.
In 2001, Dolly was diagnosed with arthritis after farm staff noticed her walking stiffly. This was successfully treated with anti-inflammatory medication, although the cause of the arthritis was never discovered.
After Dolly gave birth to her last lambs in September 2000, it was discovered that she had become infected by a virus called Jaagsiekte sheep retrovirus (JSRV), which causes lung cancer in sheep. Other sheep at the Roslin Institute had also been infected with JSRV in the same outbreak.
Dolly continued to have a normal quality of life until February 2003, when she developed a cough. A CT scan showed tumours growing in her lungs and the decision was made to euthanise Dolly rather than risk her suffering. Dolly was put to sleep on 14 February 2003, at the age of six.
Where is Dolly now?
After her death the Roslin Institute donated Dolly’s body to the National Museum of Scotland in Edinburgh, where she has become one of the museum’s most popular exhibits.
Dolly meets the media Image copyright: Murdo Macleod