|MadSci Network: Genetics|
I think the breaking apart and shortning has to do with the telomere sequences. Those DNA-sequences (rich in G's) are present in (probably) all cells of all higher organisms and are located at the end of the chromosomes. When the DNA is copied (replicated), these ends are not completely copied. Compare this with a big pile of paper which is copied several times. The white backpage (notes) will soon be left out.
However, in certain organs, the chromosomes may not age. Examples can be the testis and ovaries. There are specific enzymes (telomerases) that have something to do with preventing the chromosomes from wearing down.
A nice review about telomeres can be found in CELL vol 87 no 3 (november 1996), pages 369-375.
So the DNA does not really break up during aging, but loses ends (like a jeans ;).
Something completely different is the breakdown of DNA during programmed cell-death (apoptosis). During this selfdestruction cycle cells will cut their DNA in nice small chunks to commit very succesfully suicide. Much about apopotosis is not known, but it may be an important mechanism in prevention of allergies, cure from diseases (eg cancer), have something to do with diseases like Multiple Sclerosis and AIDS, etc.
However, keep in mind that apoptosis is not causes (primarily) by aging!
So the ends of the chromosomes of Dolly may be old, the genes itself are not old. However, it would be nice to know how these older chromosomes will influence the eventual age Dolly will reach.
Try the links in the MadSci Library for more information on Genetics.