This installment of Comic Book Legends Revealed tells about what led up to the reveal of Magneto being the father of Scarlet Witch and Quicksilver.  It's the second of three items in the column.

http://goodcomics.comicbookresources.com/2010/05/13/comic-bo ok-legends-revealed-260/

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That's a neat point. How would you deal with mutants in the Marvel universe having children? (Whizzer wasn't a mutant was he? He's the one who got his powers from Mongoose blood right?)

Would those children be more likely to be mutants? Would they be guranteed to be mutants but with random powers? Or would they be normal humans? Would mutants be sterile like mules?

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When Stan and Jack created the X-Men the premise was very simple: mutants were people who were born with a kink in their DNA which eventually (around puberty) manifested itself in strange and usually most inconvenient powers -- eye beams, wings, enormous hands and feet, etc.

This made mutants different from the FF, or Spider-Man, who had been exposed to some extraordinary set of circumstances which had created a kink in their DNA.

So it was really simple: born that way (or at least with the potential) = mutant. Picked it up along the way somewhere = non-mutant variant.

The question of mutants breeding and whether this would create other mutants should be equally simple. As a way of explaining why the Sentinels had trouble identifying Wolverine as a mutant, I suggested (and Chris and I were working toward revealing) that Sabretooth was Logan's father, and that HIS mutation had bred true. Wolverine was not a mutant, he was a whole new species.

People have often asked what it is that makes Namor a "mutant". He is a HYBRID, they say, possessing abilities from both his parents. Ah, but neither of his parents had wings on their heels, did they? THAT is what makes him a mutant!

Franklin Richards is a mutant, because the set of powers he got are derived from neither parent (except to the extent that they were both zapped by cosmic rays and became, themselves, non-mutant variants.)

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JB it was in the pages of the X-Men...#125 I believe...right before the Proteus Saga. That was a shock to me as well

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You are correct! Roger and I thought about doing it in THE AVENGERS, but decided instead to add a pages to an X-MEN tale. Either way, tho, that was all there was -- and all that was ever intended!

Wasn't there an idea floating around Marvel back when that anybody who had gotten superpowers was pretty much a latent mutant that exposure to some trauma had brought about? Something unique in the body chemistry, as it were?

Like, how that spider bite or gamma bomb explosion would have killed anyone else but not Peter Parker or Bruce Banner?  Or even the drug experiment that killed all other kids except Cloak and Dagger, because they were latent mutants.

I'm not sure where I picked up this idea, but it seems it was implied in at least a couple of books back in the late 80's/early 90's.