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. Author manuscript; available in PMC: 2018 Jan 1.
Published in final edited form as: Ageing Res Rev. 2016 Apr 30;33:89–104. doi: 10.1016/j.arr.2016.04.006

Figure 3.

Figure 3

Clonal expansion and heteroplasmy. Individual mitochondria contain many copies of mtDNA. During replication, a mutation and/or deletion can occur. This damage accumulates by clonal expansion. When the fraction of mutated mtDNA relative to total mtDNA exceeds 60% depending on the tissue affected, dysfunction and disease are measurable. The mitochondria are represented as the brown ovals, green circles are healthy mtDNA and red circles are damaged mtDNA. The yellow lightening bolt represents damage occurring during replication and the blue circles represent the replication machinery.