Thursday, May 27, 1999 Published at 13:22 GMT 14:22 UK
Is Dolly old before her time?
How old is Dolly?
The possibility that the sheep may die early has been raised after a study of her genetics by some of the same scientists who created the clone in 1996.
They report in the journal Nature that the structures are slightly shorter than would be expected in a sheep of her age born normally.
"All we're saying is that yes, as we and others expected, this animal started off with shorter telomeres," Dr Alan Coleman, research director at PPL Therapeutics told the BBC.
"In fact, if sheep like Dolly and other mammals made by this [cloning] technique are continually shown to be perfectly healthy and not age prematurely, that would just prove that the whole link between the telomeres and ageing is an unreliable one and not worth worrying about."
Telomeres are nubs of protein and nucleic acid that cap the ends of chromosomes, the structures in cells that bundle up all the DNA.
The telomeres are produced during embryonic development but start to crumble away as cells mature and divide. When the erosion is complete, so the theory goes, the cell commits suicide.
Dolly's shortened telomeres would seem to stem from two factors:
Dr Coleman says the research will need to be followed up on many more cloned animals. But from what they know already, he says he would not recommend cloning clones because this would only amplify any problems that might exist.
Scientists believe they can ally cloning and stem cells to create perfect-match transplant tissue.
They envisage, for example, leukaemia victims being able to provide their own bone marrow transplants.
"Undoubtedly they would go down dramatically," says Dr Alan Coleman. "If you put these cells back into a human, you would be asking yourself how long they would last. How would they behave if they have been having all this erosion taking place at the end of their chromosomes?"
He believes one thing is certain - Dolly and all the other clones now being created around the world will tell us a lot more about the lifecycle of cells and the ageing process.