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Figure 1 | Biology Direct

Figure 1

From: Mitochondrial DNA, chloroplast DNA and the origins of development in eukaryotic organisms

Figure 1

DNA repair cost during the evolution of development. The single cell of a protist is metabolically active (A) and generates ROS and oxidative stress during mitochondrial respiration. Oxidative stress leads to mtDNA damage that must be fully repaired at a cost of 100. An organism containing two A cells gains no selective advantage. Conversion of one A cell to a metabolically quiescent (Q) cell reduces the damage load and repair cost, but this two-celled organism gains no advantage. If the Q cell acts as a germ cell, the organism gains an advantage by lowering the repair cost in its A cell, even though some A-cell mtDNA remains unrepaired and may be degraded. At this point, many evolutionary "experiments" can occur with multicellular embryos, and those allowing further reduction in cost-per-A-cell gain a large advantage. For example, the multi-copy nature of mtDNA in humans provides sufficient mtDNA of "good enough" quality to reach sexual maturity, after which degenerating mitochondrial function leads to aging symptoms. An analogous scenario can be made for cpDNA.

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