Quote:
Originally posted by jaguar
I'm no expert but from what I read the cells in dolly aged incredibly fast, I think they may have started at her mother's age or something. Like a counter that needed to be reset or something. That of course it the highly scientific version 
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That's very close to true, from what I understand.
The chromosomes in cells duplicate themselves every time a cell divides. The duplicates are identical to the original except for the ends of the chromosomes, called the telomeres. After each division, the telomeres get shorter. Cells are programmed to self destruct if their telomeres are too short. This means that the total number of divisions an animal cell can undergo is fixed at a certain number from the moment of conception.
Dolly's original egg cell was really some cell from her parent that was 'zapped' or something in order to make it think it was a fertilized egg. While its DNA is intact, it still has the shortened telomeres of a grown sheep, so Dolly may have been physically young, but her cells thought they were old.
For true cloning (or immortality) we have to discover how to reset this telomeres timer.