Dolly the Sheep Cloned
In February 1997, scientists at the Roslin Institute near Edinburgh, Scotland, announced that they had produced a lamb named Dolly, the first mammal cloned from a cell taken from an adult animal. Dolly had been born the previous July, and the news was held back until the research could be published. Her existence showed that a specialized adult cell could be reprogrammed to produce an entire new organism, overturning a long-held assumption in biology and igniting a worldwide debate about the ethics of cloning.
The background lay in decades of work on nuclear transfer, a technique in which the nucleus of one cell is placed into an egg cell whose own nucleus has been removed. In the 1950s and 1960s, researchers had cloned frogs this way, though mostly using cells from embryos or tadpoles. Many biologists believed that in mammals, cells became so specialized as they matured that their genetic programming could not be reversed. Earlier mammal clones had been made only from embryonic cells. The Roslin team, led by Ian Wilmut and Keith Campbell, working with the company PPL Therapeutics, aimed partly to find better ways of producing genetically modified animals for medical purposes, such as livestock that make useful human proteins in their milk.
To create Dolly, the researchers took a cell from the udder of an adult Finn Dorset ewe and encouraged it to enter a resting state, which appeared to help its genes be reprogrammed. They fused it with an egg cell from a Scottish Blackface ewe that had its nucleus removed, then stimulated the combined cell to divide and implanted the resulting embryo in a surrogate mother. Dolly was one of very few successes from several hundred attempts, which showed how inefficient the method was. She was named, as commonly reported, after the singer Dolly Parton.
Dolly lived at Roslin and bore several lambs through ordinary breeding. She developed arthritis and a progressive lung disease, and was euthanized in February 2003 at about six years old, roughly half the typical lifespan of her breed. Whether her cloned origin contributed to her health problems remains uncertain, and later studies of other cloned animals have given mixed results.
The consequences were wide-ranging. Dolly prompted governments and ethicists to consider the possibility of human cloning, and many countries introduced laws or guidelines restricting it. Scientifically, her birth encouraged research into cell reprogramming, which contributed to later breakthroughs such as induced pluripotent stem cells, for which Shinya Yamanaka shared a Nobel Prize in 2012. Her preserved body is displayed at the National Museum of Scotland in Edinburgh.