(via TEDEd) Inside our cells, each of us has a second set of genes completely separate from our 23 pairs of chromosomes. And this isn’t just true for humans— it’s true of every animal, plant, and fungus on Earth. This second genome belongs to our mitochondria, an organelle inside our cells. So why are they so different from anything else in our bodies? Devin Shuman explores the purpose of mitochondrial DNA.