The inheritance of viable mitochondria

Mitochondria cannot be produced de novo by the cell, but are inherited across generations. Their peculiar genetics (multiple genomes per cell, no meiosis, replication independent from cell cycle, high mutation rate) and the possible exposition to Reactive Oxygen Species (ROS) are predicted to produce a fast accumulation of deleterious mutations, a phenomenon known as Müller’s ratchet. Nonetheless, mitochondrial genomes persist accurately over million years. How is a viable mitochondrial genetic information preserved? To answer this question we review the following relevant topics: 1) the sources of mtDNA mutation (replication and ROS); 2) the origin of mitochondrial membrane potential; 3) the activity of germ line mitochondria; 4) the mitochondrial bottleneck; 5) mtDNA drift and selection. Finally we discuss such topics in the light of an unusual biological system (Doubly Uniparental Inheritance of mitochondria, DUI), in which also sperm mtDNA is regularly transmitted to the progeny.