Heteroplasmy

Heteroplasmy is the presence of a mixture of more than one type of an organellar genome (mitochondrial DNA (mtDNA) or plastid DNA) within a cell or individual. It is a factor for the severity of mitochondrial diseases. Since most eukaryotic cells contain many hundreds of mitochondria with hundreds of copies of mtDNA, it is possible and indeed very frequent for mutations to affect only some mitochondria while others are unaffected. Heteroplasmy can be beneficial rather than detrimental insofar as centenarians show a higher than average degree of heteroplasmy.