Dolly was a Finn Dorset lamb with no father. Her genetic material came entirely from a single cell taken from the udder of another sheep. The cell had been fused with an unfertilized egg cell stripped of its own nucleus. After 277 attempts, one reconstructed egg developed into an embryo, which was implanted into a surrogate mother. Dolly was born at the Roslin Institute in Scotland. Her existence was kept secret for seven months.
Her birth overturned a central dogma of developmental biology. Most scientists believed the DNA in a specialized adult cell was irreversibly programmed and could not be used to generate a new, complete organism. Dolly proved that cell differentiation was not a one-way street. The technique, somatic cell nuclear transfer, showed a mature cell's nucleus could be reprogrammed to an embryonic state.
The event is often misunderstood as the first cloning of an animal. It was not. Scientists had cloned frogs from embryonic cells decades earlier. Dolly's distinction was her origin: an adult somatic cell. Her name, suggested by a stockman who knew the cell came from a mammary gland, referenced the singer Dolly Parton. The choice was both a private joke and a deflection.
Dolly lived a monitored life, giving birth to six lambs. She developed arthritis and a lung disease, and was euthanized in 2003 at age six, about half the typical lifespan for her breed. Her premature death sparked debates about the health of cloned animals. The technology she pioneered led to advances in stem cell research and regenerative medicine, but also to ethical debates about human cloning that remain unresolved. Her preserved body is on display at the National Museum of Scotland.