.. Not nessesarily. I just had an amusing thought. The number one use of polyjuice is quite obviously as a sex toy, right? Depending on how deep the transformation goes, it is entirely possible that the genetic lines of wizardry if anyone ever tested them would be enormously confusing, and a lot of squibs are technically the decendants of Jane Russell and Rudolph Valentino.

Probably! That or a mutation, anyway. But a few weeks ago I read about an interesting situation * in which a parent with AB blood and one with A blood can have an O child without adultery, because of another gene that sometimes suppresses the A and B antigens. That wouldn't allow for varying power levels with blood purity, and would sort of be still "one thing that makes you a wizard."

• I can't remember the name, and would appreciate if someone could remind me.

Go, Mom.

if Harry's genetic theory is correct, doesn't a squib child of a wizarding couple imply that Mom was getting some on the side?

Not necessarily. Genetic code changes in ways that do not make an nonviable specimen now and then.

Adultery is more likely, though.

doesn't a squib child of a wizarding couple imply that Mom was getting some on the side?

Accurate deduction! Here, have a cookie.