Summary of this review paper, entitled "The origin and early evolution of mitochondria"
- Organism with genetically "richest" mitochondrial genome (most likely resembles ancestral protist that underwent symbiosis) is called Reclinomonas americana
- Like viruses, mitochondrial genomes underwent "reductive evolution," in which their genomes decreased in size by throwing out genetic information that was redundant within the host cell's genome
- Genome sequencing alludes to the possibility that ALL mitochondria are derived from a single mitochondrion, meaning that this relationship arose only once in evolution
- While it is not clear when exactly the mitochondrion entered the eukaryotic cell, the evidence is clear that they primarily evolved together to create the Eukarya domain
- Mitchondria likely arose from a parasitic intracellular alpha-proteobacteria
While all of this is exciting, the evidence needs to be considered with a skeptical frame of mind. Much of the data to support the claims above came from genome sequencing, and the parts determined to be ancestral to the original mitochondrion may well just be ancestral to the universal common ancestor (for argument can be made that some of the genetic material in the mitochondrion that was considered in these studies have very far relatives in bacteria, archea, and eukarya).
So while it was an interesting read, and I think a lot was learned, not a lot was definitively claimed. But so is science.