MadSci Network: Molecular Biology

Re: Dolly the Cloned Sheep. What about Extra-nuclear genetic Material?

Area: Molecular Biology
Posted By: Wayde Weston, Faculty Pathology, Anatomy, and Cell Biology
Date: Mon Jul 7 08:19:02 1997
Area of science: Molecular Biology
ID: 867017857.Mb

Hi Paul - Good questions. Mitochondria, as you know, are maternally inherited. The mitochondria present in the oocyte are the "parents", so to speak, of the mitochondria present in the cells of the fully developed animal. While Dolly the Cloned Sheep's nuclear genome was obtained in a somewhat unconventional manner, her mitochondria are all descended from those present in the donor oocyte - same as any other sheep. So there shouldn't be any question of the mitochondria being older or less viable than a conventionally bred sheep - they are just the same. Since her mitochondrial genome is likely to be slightly different than that of the nucleus donor, I suppose you could say that Dolly isn't an exact genetic duplicate of her "mother", but I think that's quibbling - it's the nuclear genome that's the primary determinant of phenotype, and this is what's been duplicated.

Regarding telomeres - yes, Dolly probably did start out life with shorter telomeres than a conventionally-conce. Whether or not this will affect the course of her life remains to be seen. Dolly's creators have stated that the cloning procedures they've developed may allow for the study of such phenomena as genomic imprinting and telomere shortening and their effects on aging (Wilmot et al, Nature 385:810-813). By herself, though, Dolly won't be providing many answers to such questions - we will need to look at a LOT more cloned sheep for differences that are apparent between "normal" and cloned animals.

For more info on mammalian cloning, check out the Nature web site (

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