And I’m not talking about an X-gene giving people powers.
Like some mutant siblings have very different powers. Look at the Guthries. Sam propels himself like a rocket, Paige tears away her skin, Jay has wings, Melody can fly unaided, etc. Okay three of the four fly in some way, but they’re all different types of flight.
On the other end of that the Scott and Alex Summers both project concussive energy in some way and are immune to each others powers. (I don’t know enough about Gabriel to add him here.)
Those are just examples of first gen mutants. It’s when mutants start having children that things actually get interesting. Like out of all of Logan’s kids only two of them inherited his powers, but with different claw arrangements and Daken got something extra as well. And of the five mongrels only two of them seem to have any powers at all. Fire Knives might have some kind of fire power (it’s actually unclear), and Cannon Foot is animalistic but can’t heal.
One out of three of Magneto’s kind inherited his powers, Wanda’s kid inherited her and Pietro’s powers, but Luna has empathic powers.
Those are all examples of just one mutant parent. When it’s two parents the kid seems to usually have a combination of their parents powers. Cable mostly has Jean’s powers, but he also has a glowing eye he probably got from Scott. Ruby has her mom’s diamond form and her dad’s eye beams, Kurt has his mother’s coloration and a weaker version of his dad’s teleportation. There are exceptions to this, but the point is over all children with two mutant parents will be mutants.
So from all of this we can determine that x-gene is recessive and the mutation it creates is mostly random but a mutant parent means a higher chance of that power. Okay all of this is fine except: