endosymbiotic hypothesis The hypothesis that the plastid and mitochondrial organelles evolved from prokaryotic endosymbionts within eukaryotic cells early in eukaryotic evolution. At least 2 endosymbiotic events are postulated, 1 each for plastid and mitochondrial origins. It is contentious whether 2 independent events could account for the mitochondria that occur in plants and those that occur in animals, the present-day mitochondria of the 2 kingdoms being quite distinct from each other genetically.

endosymbiotic hypothesis The hypothesis that the plastid and mitochondrial organelles evolved from prokaryotic endosymbionts within eukaryotic cells early in eukaryotic evolution. At least two endosymbiotic events are postulated, one each for plastid and mitochondrial origins. It is contentious whether two independent events could account for the mitochondria that occur in plants and those that occur in animals, the present-day mitochondria of the two kingdoms being quite distinct from each other genetically.