Figure 1.

Mechanisms of inheritance of mtDNA mutations. Each mitochondrion consists of multiple copies of mtDNA, some of which may harbor harmful mutations. Upon mitochondrial fission, fusion, or mtDNA replication, these mtDNA molecules may be randomly segregated to daughter mitochondria, resulting in either reduced or increased levels of heteroplasmy. The contribution of heteroplasmy to disease development is difficult to study, as the disease threshold for each mutation may be different and may lead to a range of clinical and sub-clinical phenotypes. (Green ovals = functional mitochondria; red = dysfunctional; blue = suboptimal function).