Mitochondrial genetics revisited.

Mitochondrial genetics started decades ago with the discovery of yeast mutants that ignored the Mendelian rules of inheritance. Today, the many known DNA sequences of this second eukaryotic genome illustrate its eccentricity in terms of informational content and functional organisation, suggesting a yet incomplete understanding of its evolution. The hereditary transmission of mitochondrial alleles relies on complex mixes of molecular and cellular mechanisms in which recombination and limited sampling, two sources of rapid genetic changes, play central roles. It is also under the influence of invasive genetic elements whose inconstant distribution in mitochondrial genomes suggests rapid turnovers in evolving populations. This susceptibility to changes contrasts with the development of specific functional interactions between the mitochondrial and nuclear genetic compartments, a trend that is prone to limit the genetic exchanges between distinct lineages. It is perhaps this opposition and the discordant inheritance between mitochondrial and nuclear genomes that best explain the maintenance of a second genome and a second independent protein synthesising machinery in eukaryotic cells.