Why do mitochondria have their own DNA?
Quick Answer
Mitochondria have their own DNA because they were once free-living bacteria that were engulfed by early cells. Their small genome is a leftover from that ancient symbiosis.
The Full Story
Mitochondria are thought to descend from an alphaproteobacterium that entered into a partnership with another cell more than 1.5 billion years ago. Over time, most of the original bacterial genes moved into the host cell nucleus, but mitochondria kept a small circular genome of their own. In humans, mitochondrial DNA is only about 16,569 base pairs long and encodes 37 genes. It is inherited almost entirely from the mother because the egg contributes most of the cytoplasm to the embryo.
Key Facts
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Suggested video title for this topic:
"The tiny leftover genome in your cells that proves an ancient merger!"