Flexi Says: Two pieces of evidence for endosymbiotic theory - (1) Mitochondria and chloroplasts contain DNA that is different from the DNA found in the cell nucleus. Instead, it is similar to the circular DNA of bacteria. (2) Mitochondria and chloroplasts are surrounded by their own plasma membranes, which are similar to bacterial membranes. The argument against the evidence is that the shape of the mitochondria genomes is not always circular, they can be linear (or straight). In this case, the DNA polymerase enzymes are not replicated completely to the end of the genetic code which leads to shorter chromosomes. Also, the replication of the circular mitochondria DNA is different from that of bacterial DNA replication.