The mitochondria ("powerhouse" of the cell) have their own DNA. Current biological theory has that they were at one time seperate bacterial organisms, that over evolutionary time established a symbiotic relationship with eukaryotic cells.
Because mitochondria genes do not recombine, it's been possible with current technology to trace all of humanity's mitochondria 200,000 years back to one prehistoric woman. Mitochondrial Eve represents a single female ancestor from whom all our mitochondrial genes are inherited.
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