Scientists: Cloned sheep Dolly has 'old' DNA

Dolly has DNA in her cells that is typical of an older animal

May 26, 1999
Web posted at: 11:14 p.m. EDT (0314 GMT)

LONDON (CNN) -- The scientists who created Dolly, the world's first cloned mammal, said Wednesday that the 3-year-old sheep has DNA in her cells typical of a much older animal.

"How old is Dolly the sheep?" mused Dr. Stephen Jones of London's University College. "Is she as old as her body age ... or is she as old as her genes?"

Researchers from Scotland's Roslin Institute and PPL Therapeutics have attempted to answer that question by measuring key pieces of Dolly's DNA called telomeres.

All chromosomes are capped with telomeres, tiny strands of DNA that scientists believe hold the key to aging. Telomeres shorten each time a cell divides, and continuously erode as an animal ages.

The researchers found that Dolly's telomeres were shorter than other 3-year-old sheep, suggesting she is genetically older than her birth date.

The findings will be published in Thursday's issue of the science journal Nature.

In 1996, Dolly became the first large animal cloned from genetic material taken from an adult egg. Roslin Institute scientists inserted a cell from a ewe's udder into an egg from the same animal after removing the egg's DNA.

The bioengineered embryo was implanted in the ewe's womb and Dolly developed as a clone of the 6-year-old sheep.

"Although Dolly the sheep is physically young and healthy .... her telomeres are about the same length as her mother's. She has aged genetically, but not in her body," Jones said.

Dolly's shortened telomeres had been predicted as one outcome of cloning, but researches are unsure if such evidence will cause her to die prematurely. Sheep have a life expectancy of 13 years.

Dolly has four offspring -- Bonnie, born in 1998, and a set of triplets this year. Genetic tests on Bonnie reveal normal telomeres. The offspring were conceived naturally and possess half their DNA from their father.

Correspondent Nic Robertson, The Associated Press and Reuters contributed to this report.

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