I have not read every single X-Men comic to ever exist, but from what I understand about the X gene, it comes from the male parent? But if that's true how are there female mutants? I have also read somewhere that it skips a generation, if that's the case how are Scott and Jean's offspring all mutants??
 
I am not entirely clear on this, so anyone who is more knowledgeable about this, feel free to comment and clarify, thanks :-)