Answer:
Believe it or not, mitochondria are their own organisms!
That’s right, they are single celled living beings that hitch a ride inside our cells for security, and in return they make our energy systems run much better than they would. This arrangement started a very long time ago, before we split from our last ancestor with plants, and long before we became multicellular. Other than this arrangement, our DNA has nothing to do with the DNA of the mitochondria (other than synergistic evolution making us more compatible with one another).
For this reason, it is easy to see how mitochondrial DNA differs from nuclear DNA.
First major difference is that we are in different kingdoms and even different super kingdoms to mitochondria (I know there are only meant to be 5 kingdoms but in biology people often use a system based off genetic differences, leading to a huge array of kingdoms that are often really distantly related). So our DNA and mitochondrial DNA share very few similarities. We both replicate our DNA using the same method and have the same base pairs, but the DNA itself says different things.
Another difference is that mitochondria generations are very fast compared to humans’, so their DNA undergoes genetic drift at a much faster rate, and changes more over time. Therefore it is much easier to locate recent changes in populations, for example the migrations out of Africa in the last 200,000 years, or the ethnic backgrounds of different African races, using mitochondrial DNA. In contrast nuclear DNA has fewer fine mutations that can be used as a map for recent events (in the last million years, say).
Mitochondria are passed down from mother to child in animals, so you will always have your mother’s mitochondrial DNA. This is why there is a mitochondrial Eve- this is the last female that is an ancestor of everyone on the planet, and therefore every human possesses direct ancestors of her mitochondria (and her nuclear DNA). In contrast we receive a 50/50 split of nuclear DNA from father and mother.
I hope this helps!
