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THE birth of Dolly鈥檚 first lamb, Bonnie, announced last week, provides
further reassurance that clones can develop into healthy animals.

But researchers at the Roslin Institute near Edinburgh, who cloned Dolly, say
it will take several months to show whether she and her offspring have escaped
chromosome abnormalities that could make them die young.

Dolly鈥檚 successful pregnancy is good news for those who want to commercialise
animal cloning. 鈥淭his suggests that clones can be founders of flocks that can be
sustained by conventional breeding,鈥� says Harry Griffin of the Roslin
Institute.

While mammalian clones have given birth before, extra questions surrounded
Dolly鈥檚 fertility because she was cloned from a cell of a six-year-old
adult鈥攂y far the oldest 鈥減arent鈥� of any clone.

One hallmark of mammalian ageing is the steady loss of sections of DNA,
called telomeres, from the ends of chromosomes. Some scientists have suggested
that because Dolly was derived from an old cell, she might have unusually short
telomeres.

鈥淚f Dolly does have shorter than normal telomeres, then it becomes an
important question whether Bonnie鈥檚 telomeres are normal,鈥� says Griffin.
Information about Dolly鈥檚 telomere length is expected later this year, and
Griffin says researchers will take a sample of Bonnie鈥檚 blood for comparison.
鈥淚t鈥檚 a complex issue and we鈥檒l need to look at a whole body of data to
understand what鈥檚 happening.鈥�