Unread postby ewuvi » April 30th, 2015, 4:12 pm
I stumbled back to the forums and people are talking genetics?!
Going to start off by saying that we don't actually have enough data to make a definite conclusion. And from a fanworks perspective that's actually great because you have so many directions you could go with this.
First of all, there is no way that Byakugan is Y-linked since Hinata and Hanabi have it. This is said with the assumption that they are both genetically typical females, but given the context I think it's a fair assumption to make. There is also no such thing as a male-exclusive x chromosome. When a male passes his x onto a daughter, then the daughter would pass that x on to half of her offspring. Hinata and Hanabi aren't X/O (so they didn't get one gene from their mom and none from their dad) because Hinata at least is fertile, and they would probably look a lot different than they do if that were the case.
It could certainly be recessive, but that would have a lot of funny consequences. Like, do they bar breeding outside of the clan? They'd basically have to. I mean if there were male Hyuuga getting the hanky panky on outside of the village during, say, missions then I would expect the Byakugan to show up eventually out there. I mean to show up in a male offspring all that would have to happen is a mother with a Hyuuga father passing down her recessive byakugan trait. It'd probably disappear after one generation, unless they got it on with another woman of Hyuuga descent in which case having kids that with the Byakugan phenotype would be 50-50 with each kid. Unless birth control is 100% effective, Konoha is really good at assassinating anyone who gets it on with a Hyuuga, or Branch men are somehow incapable of having sex without permission, then another hidden village finding and collecting these kids to get the Byakugan wouldn't be that improbable.
I mean obviously the branch Hyuuga are fertile and can have sex, because Neji exists. Forcing them to get permission before being able to have sex would be pretty humiliating and further strip the dignity of that entire part of the family, so it's interesting that there appears to be a sudden reconciliation between the two branches of the family. Though I suppose they'd also have to intermarry with the branch family which would be weird. Like...HinataXNeji might be possible in this scheme since they're about the same age; but then Neji would have a chance to effectively be the clan head so...I don't know. Weird stuff lies that way.
Also so much inbreeding would be going down this way that you'd think they'd have a reputation for being ill or crazy after as many generations would need to exist to make a large, purely Byakugan phenotype clan.
It actually could also be dominant, which would open up a different can of worms. We don't actually see Hinata or Neji's mothers at any point so it's possible that one of them had a mother that wasn't a member of the clan. It would have to have been Hinata's unless we have an instance where someone has an unexpressed dominant allele which can actually happen, although it's very rare. Anyways, if it were Hinata's mom, then perhaps reason why her Byakugan isn't as "good" as Neji's could be a problem of co-dominance between a non-Hyuuga mother and her father. She doesn't have any brothers but if she did and they didn't have the Byakugan at all what would have happened to him? This might also explain why in a society that is as sexist as the one in Naruto's appears to be, a female heir isn't surprising in the Hyuuga clan. They were disappointed in her weakness, not her gender, after all.
If it were Neji's mom then there would be the whole "how did that gene not get expressed in his mom what the hell is going on, genetics is freakish" thing and it might explain some of the weirdness that the rest of the clan seems to have about him in addition to him being brilliant.
Limiting breeding outside of the clan would still be an issue in this case, although more for keeping the Byakugan to themselves rather than also being necessary for the retention of it in the clan.
Another possibility is that Hinata's just a freak and her ovum were screwed up by Kyuubi's magical chakra or something to that effect. Her kids should have had byakugan but don't, and no one says anything to her or them about it because that would basically be suicide.
Honestly though, it could have just been that the author doesn't know anything about genetics and decided that Naruto's genes would be dominant no matter what cause his genes are totally going to overpower Hinata's cause that's totally how genetics works. Except when they have daughters. Then they can have dark hair (How does Bolt have blonde hair I don't understand). Or maybe he didn't even give it any thought at all and decided that since their last names wouldn't be Hyuuga they wouldn't have Byakugan and he liked their designs without creepy, pupil-less eyes more anyways.
Also as jgkitarel got at, genetic interactions are weird, mistakes do happen so variability is inevitable, normally dominant traits can be silenced very occasionally, etc. etc. etc.
tl;dr: There are a boat-load of explanations as to why Himawari and Bolt might not have Byakugan and each of them would lead to interesting implications that might be fun to explore in someone's fanwork.