Mitochondria contains it's own DNA. It's structure is a bit different from that of the chromosomes found in the eukaryotic nucleus. From my understanding, it supports the endosymbiotic theory because it contains characteristics similar to single-celled prokaryotic cells despite it being classified as an eukaryotic cell.
Another function of the mitochondria that supports the endosymbiotic theory is that the mitochondria are responsible for their own reproduction. Eukaryotic cells are duplicated by its nucleus, however, despite it being classified as an eukaryotic cell, the mitochondria does all the work on it's own. Again, it supports the endosymbiotic theory because it contains characteristics similar to single-celled prokaryotic cells despite it being classified as an eukaryotic cell.
