Seven years after the death of Dolly, a female sheep who was the first to be cloned using an adult somatic cell, four new sheep have been cloned using Dolly's frozen tissue sample that has been sitting in a freezer since her death in 2003.

Professor Keith Campbell, one of the original biologists who cloned Dolly, is keeping the four new quads on his land at the University of Nottingham as pets. They have been nicknamed "the Dollies," since they are exact copies of Dolly genetically. 

In 1996, Dolly, who was named after the country singer Dolly Parton, was cloned at the Roslin Institute near Edinburgh in Scotland. She was the first mammal to be cloned using an adult cell from a mammary gland, and was praised as a scientific phenomenon in headlines worldwide. But as she aged, Dolly experienced several health complications such as arthritis and advanced lung disease. At the young age of six, Dolly was put down because of her poor health. 

But Dolly lives on. Her leftover sample of tissue has remained in the freezer all these years later, and now four exact replicas carry her DNA. 

Campbell cloned the Dollies to see if improvements made to the cloning technique prevented the health problems that Dolly suffered within the new sheep. So far, Campbell says the Dollies are doing fine and that they are being watched very closely. 

"We are not doing anything to them," said Campbell. "They have no health concerns and they show none of the signs of developing the arthritis that Dolly had."

In addition to being healthier than Dolly, the Dollies were also easier to clone. During Dolly's cloning process, 277 eggs were used to create 29 embryos and only Dolly survived. With the Dollies, only five embryos were required to produce each of the four Dollies. 

The Dollies are already three and a half years old, but Campbell did not mention their existence until a recent lecture at the European Parliament debate on cloning and animal welfare. He is looking to publish further detail on the Dollies in a scientific journal, noting that the cloning technology is improving but not yet perfect. 

Several different groups are taking interest in the Dollies, such as animal welfare campaigners and stem cell scientists. Animal welfare campaigners have detailed the suffering that clones and surrogates experience during the cloning process, and Peter Stevenson of Compassion in World Farming has even said that "cloning is a welfare disaster."

Despite the critics, Campbell insists that improved technology has put the Dollies at less of a risk of health problems, and that the four sheep "got the life of Reilly - they potter around and get fed."