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THE ends of Dolly the cloned sheep鈥檚 chromosomes are shorter than those of
normal sheep of the same age. This suggests that she inherited some of the wear
and tear suffered by her six-year-old mother鈥檚 cells.

Whenever a cell divides, the end of its chromosomes, called telomeres, erode
away. When they wear down to a critical length, the cell stops dividing. Older
animals have shorter telomeres, and biologists consider telomere shortening a
hallmark of ageing.

So when a team at the Roslin Institute near Edinburgh turned an adult cell
into Dolly, scientists wanted to know about her telomeres. Now the Roslin team
and the affiliated company PPL Therapeutics say that Dolly鈥檚 telomeres are
shorter than those of two sheep cloned from embryonic cells鈥攁nd all of the
clones鈥� telomeres are shorter than those of normal sheep (Nature, vol
399, p 316).

For the time being, Dolly seems healthy. And biologists will need to study
many cloned animals before they know whether their shortened telomeres will make
them age more quickly.

The problem could get worse if cloning is carried out over several
generations. But normal reproduction seems to repair the shortened telomeres:
Dolly鈥檚 first daughter, a lamb called Bonnie conceived in the traditional way,
has normal chromosomes.

Given the uncertainties, however, Alan Colman of PPL Therapeutics says the
findings provide 鈥渁nother good piece of evidence to make people shy away from
human cloning鈥�.