From Jim Cummins
So all Dolly’s mitochondria come from the egg to which the udder cell nucleus
was added, and not from the udder cell
(4 September, p 5). The selective
disappearance of donated mitochondria is not such a great surprise. We know from
work using chimeric mice, whose bodies are made up of tissues with different
genotypes that some forms of mitochondria will preferentially persist in some
tissues while others disappear.
The rapidly mutating mitochondria rely heavily on nuclear-encoded genes for
much of their function. There is a need for close concordance between nuclear
and mitochondrial genes. This means that each cell is unlikely to tolerate
having more than one sort of mitochondria in its cytoplasm, and helps to explain
why organisms inherit mitochondria from only one parent, generally the
mother.
As an analogy, mitochondria are slave organelles carrying out the dirty and
dangerous business of energy production. No sensible master will tolerate
democracy among their slaves. As the egg’s mitochondria have been carefully
groomed to support embryonic development, it is not surprising that the
interlopers were cast out.
cummins@central.murdoch.edu.au
