Evolution of mitochondrial gene content: gene loss and transfer to the nucleusadams2003mitochondrial
Eukaryotic relationships with mitochondria are largely accepted to be the result of an endosymbiotic event between an ancestral eukaryote and a "proto-mitochondrion". Since this event, genes encoding functional aspects of the mitochondrion have been transferred to the eukaryotic nucleus -- for reasons that are unclear but may be related to increased genetic control and/or stability. This review describes current understanding of this process, including the different extents to which it has occurred in different lineages across life. Rickettsia looks perhaps a bit like a precursor mitochondrion; Reclinomonas americana has retained more (67) mitochondrial protein genes than other organisms; animals seem to have stabilised at 13 protein and 22 tRNA genes.