Moved from "The Executioner" because it was getting off-topic:
Heh. I hate to keep nitpicking details that are not really part of the original question... well, no, I don't. I'm a canon nitpicker, I can't help it.Originally Posted by Equinox Chick
Has Rowling ever actually said that having a Squib in your family is proof of Muggle blood? Because while that's a reasonable supposition, I'm not convinced it's necessarily true. Maybe purebloods can be born Squibs on occasion, just like someone without a family history of deafness can nonetheless be born deaf.
Now, Ron did point out that there really isn't any such thing as a "pureblood" anyway, since pretty much all wizarding families have Muggles in their family trees (else the wizarding world would have disappeared long ago).
But, to the extent that Rowling has written about wizarding genetics (with her admittedly dodgy grasp of science), I don't think she's established that a Squib is proof of Muggle ancestory.