This question already has an answer here:
As I understand it, both the X-Men and the Inhumans receive their powers due to their innate genetics (as opposed to supers that got it from an external source, like Spider-Man who got it from a radioactive spider).
In the mainstream, Earth-616 comics universe, what is the difference between these two groups? Do they have different sets of genes that both happen to express themselves as superpowers? Or is there some other important difference?