Endosymbiotic theory

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The term endosymbiotic theory is used to refer to any theory that a particular organelle or other substructure in a cell is evolutionarily descended from a living organism (specifically, a prokaryote) that lived as an endosymbiont inside the cell.

There are endosymbiotic theories associated with the following organelles:

Organelle Endosymbiotic theory
mitochondrion endosymbiotic theory of mitochondrial origin
plastid endosymbiotic theory of plastid origin

Evidence used to support endosymbiotic theories

Evidence type What it should be to support the endosymbiotic theory
organelle size The organelle size should be in the size range for prokaryotic cells similar to the claimed endosymbiont
organelle replication The organelle should have its own DNA/RNA with coding and other features similar to prokaryotic cells similar to the claimed endosymbiont
membranes and regulation of material flow The presence of a double membrane provides strong support for the endosymbiotic theory, because, evolutionarily, the inner membrane would be descended from the membrane of the endosymbiont, and the outer membrane would be descended from the membrane of the host