That's not how genetics works.
So I'd imagine anything passed down by 'genetics' would not work that way. Unless you're saying the Magical Vampire Killilng power resides in the Belmonts' testicles. And even, any male with Belmont DNA would get the power, regardless of whether the parent that's a Belmont is male or female.
Ha ha! Magic Testicles.
But it isn't genetics, is it? Wasn't the "Vampire Hunting Gene" something brought up with the American version of Dracula's Curse(just like the Poltergeist King)?
I always saw the main line of power being passed down from father to son as being similar to various curses of lore. Infamous male-only curse would be the "plague of the first born son" in the Bible. Sometimes magical curses(or blessings) aren't really PC in their working.
While I don't doubt female Belmonts DO retain some holy power within themselves(are still probably more blessed as warriors than any common human man), the ability to wield the VK whip is reserved for a male of the main Belmont family line, who carries the "Belmont" surname and passes it down to a male heir so the whip stays in the family.
Though, yeah, I can't help to think that it's both a blessing and a curse. The Morris clan is blessed by being blood relatives of the Belmont clan, but cannot wield the VK whip without sacrificing their own life. The Belmonts, themselves, cannot escape their destiny, and are always vampire killers. When taking Leon into account, he basically cursed his descendants. That they will always hunt Mathias until he's finally defeated. Sure, we think, "How cool it must be to be a vampire hunter!", but what if Simon always wanted to be a peaceful sheep herder?