<unk>  is the presence of more than one type of organellar genome (mitochondrial DNA or plastid DNA) within a cell or individual. It is an important factor in considering the severity of mitochondrial diseases. Because most eukaryotic cells contain many hundreds of mitochondria with hundreds of copies of mitochondrial DNA, it is common for mutations to affect only some mitochondria, leaving most unaffected. Although detrimental scenarios are well-studied,<unk>  can also be beneficial. For example, centenarians show a higher than average degree of<unk> . Microheteroplasmy is present in most individuals. This refers to hundreds of independent mutations in one organism, with each mutation found in about 1–2% of all mitochondrial genomes.
Heteroplasmy
Allelic heterogeneity
Genetic heterogeneity
Variegation 
Phenotypic heterogeneity
Dynamic mutation
Non-Mendelian inheritance
Low copy repeats