If the original cells used to create the clone came from an adult animal (as in the case of Dolly the Sheep), then they will have undergone many cell divisions before the clone was brought into existence. Cell division (one cell splits to make two) is at the heart of all growth and development, but every time a cell divides a part of its chromosome, the telomere, is shortened. I don’t think anyone yet knows why, but the length of the telomere is like an ageing “clock”, and whether it is a cause or effect of of ageing it seems that Dolly’s cells may have shown signs of age from the start. So this might lead clones to live shorter lives.
Hi popthebottle – this is a very topical question since the Nobel prize was awarded last year to three scientists for work related to this area: Elizabeth Blackburn, Carol Greider and Jack Schostak.
There may be several causes but one contributory factor, as I understand it, it to do with the length of your telomeres. These are sequences of repetitive DNA found at the ends of your chromosomes – repetitive in that the pattern of A, G, C and T letters repeats. These telomere sequences are used every time a cell divides (as your grow and age) in order to help to copy your chromosomes (i.e. your DNA).
But as you get older, the telomere sequences get shorter. When they get too short, this makes it difficult for cells to divide and I think that must contribute to aging and, ultimately, death.
So a clone, which is an animal that is derived from an adult cell, is born with telomeres that are shorter that what it would have if it had been born naturally.
As a result, the ‘sell by’ date on their cells is already quite advanced – so they don’t live as long as normal animals.