It's not a given that Anya was human, as she died before she had an opportunity to manifest mutant powers, but it's possible she was. As I mentioned in my post, Magneto was probably born to human parents, as neither of his parents ever manifested mutant powers in canon, therefore he could not have been an XX SS, so he would've been capable of producing a human child. Unless one parent is XX SS (and therefore will always produce mutant offspring) it's a roll of the genetic dice as to what the children will be.

I absolutely believe mutancy is a polygenic trait, as there's no way to explain multiple mutant powers, secondary mutations, or how second-generation mutants can have different powers from their parents otherwise. BTW, I strongly suspect that without Chthon's magical influence during her birth Scarlet Witch would've been magnetokinetic like her father and half-sister, Polaris.

I will forever lament the lack of third-generation mutants to study, as the handful we have either have some kind of MAD SCIENCE tampering going on, or they're mixed with some alien species or another human subspecies. Clearly the X-Men need to get busy and make me some little mutants to study.