Phe inheritance of mitochondrial DNA heteroplasmy: random drift, selectionor both?

The mammalian mitochondrial genome (mtDNA) is a small double-stranded DNA m olecule that is exclusively transmitted down the maternal line, Pathogenic mtDNA mutations are usually heteroplasmic, with a mixture of mutant and wil d-type mtDNA within the same organism. A woman harbouring one of these muta tions transmits a variable amount of mutant mtDNA to each offspring. This c an result in a healthy child or an infant with a devastating and fatal neur ological disorder. Understanding the biological basis of this uncertainty i s one of the principal challenges facing scientists and clinicians in the f ield of mitochondrial genetics.