system
Given the following post, respond as if you're commenting on Reddit:
human
Why do mitochondria have their own separate 'mitochondrial DNA'?

Do other cells or organelles have their own separate DNA? Is it some relic of the very distant past?
gpt
It is in fact a relic of the past. Early in the history of life, we believe the eukaryotic ancestor enveloped an aerobic bacterium, but rather than digesting it, it lived within the cell. Eventually, the eukaryote and the bacterium would exchange genetic material, and the two would become interdependent on one another. This is what we call endosymbiotic theory. And there is predicted to be 2 primary events (mitochondria from aerobic bacteria, and chloroplasts from cyanobacteria), and 3 secondary events (green algae and their chloroplasts being taken up by other eukaryotes).

You can recognize these events through a few characteristics: extranuclear, circular genomes, independent reproductive cycles, and multiple membranes.