Just thought I'd drop in my two cents, for internal consistency within the Sonora world, that my family is a bunch of mongrels so we have extensive examples of wizard-muggle pairings (who are not always married).
Basically, it depends on plot requirements.
Generally speaking though, it's not guaranteed. For Derwent One and his two muggle dalliances, he got 3 kids, two magical, one not. For the girls descending from Regina, all were magical, but who their fathers were is anybody's guess - there were probably some muggles in there, though. My cousin, Simon, who's the groundskeeper here, has a dad who is some kind of nonmagical half-muggle, half-squib whatever he is, and Simon's mom is pretty near a squib herself though she does have the ability to cast really really simple charms. Him and his brother are both perfectly competent at magic. Overall, the clan is about half and half for magic users and non magic users, though. Maybe a *little* heavy on the magic side. I haven't really counted recently.