Why does mitochondria have its own DNA? originally appeared on Quora, the place to gain and share knowledge, empowering people to learn from others and better understand the world. You can follow Quora on Twitter, Facebook, and Google Plus.

Mitochondria are primitive bacteria which took to living inside other cells billions of years ago. They enable the cells they live inside to process energy more efficiently, and without them large multi-cellular organisms would probably be impossible. They gave up both independent life and independent reproduction a long time ago and can now only exist inside other cells, and reproduce by being cloned during the production of egg cells (or equivalent) and passed on to the offspring of the host, evolving only through gradual mutation, but they do still have their own tiny internal structures and DNA.

Chloroplasts, which enable plants to photosynthesize, are another type of symbiotic bacterium living inside more complex cells. Neither should be confused with the symbiotic bacteria which live in the guts of animals and help them to digest food - these swim around freely in the gut and reproduce by binary fission on their own schedule just as they would in a pond, rather than being locked into the cells of the host.

I've been told that some fungi have mitochondria which have no internal DNA, meaning that the genes which code for the production and form of their mitochondria must somehow have been transferred into the DNA of the fungus itself.

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