Graphical representation of the effect of various mitochondrial gene therapeutic approaches on mitochondrial heteroplasmy. A cell can go from homoplasmic wild type (dark Green) to homoplasmic mutant (dark ochre) and pass stages of heteroplasmy where either wild type (light green) or mutant (light ochre) mtDNA is dominant. The threshold determines the transition from normal phenotype to mutant phenotype. Ovals represent therapeutic intervention and rectangles represent natural processes. Arrows that do not contact the DNA boxes indicate that the process does not change the ratio or content of DNA. Figure recreated based on a corresponding figure in [145].