Random because because: Okay, so Gwen, Ben, and Ken have green eyes. We know this to be true.
I mentioned in a reply to a post, last week I think, that that's a whole thing. Basically eye color in humans- so far as I understand it I am not an expert by any means I just read shit- is mostly controlled by one gene that either says 'you have a lot of melanin in there and have brown eyes' or 'you don't have a lot of melanin in there and have blue eyes'. With blue being recessive against brown. Eyes' color is also determined to a lesser degree by a load of other genes that essentially go either 'make eye more melanin-y' or 'make eye less melanin-y'. This is why you can have two people with blue eyes have a brown-eyed kid and vice versa. Green and hazel, meanwhile, are tied to a whole separate gene that basically determines whether or not the eye makes yellow pigment. I don't know the dominance structure of it, but I'm gonna assume recessive because green and hazel are rarer than the others.
"Achi why-" listen I'm rolling
So, Gwen, Ben, and Ken have green eyes. This means we can assume they're all fucking... (gods I can't remember the proper designation for the gene...li? maybe?) We'll just call it y/y for this. They have the 'make yellow' gene turned on.
Now, Max, Carl, and Frank? All seem to have brown eyes. So more likely than not they all have a B. There could be 'make color darker' genes at play, but I don't think that's too likely given how much brown we see in the family (seriously, Vera, Gordon, Joel, Betty-Jean's eyes are blue but otherwise? it's a lot of brown in the family and so probably a B gene). What else Max has doesn't really matter, just that he passed that B on to his sons.
Verdona, meanwhile, things get interesting, because in her human shape her eyes are blue. A pretty dark blue too, she may be making herself some 'make color darker' genes. But what's interesting here is that this means while her sons likely both inherited a b gene from her (especially if she's got 'make color darker' genes it's more than likely she's going with b/b and so they're both B/b), they could have gotten a y from either her or Max. And, I would kind of have to assume it's Max, I mean how likely is it that she would, in taking human shape, give herself a carried recessive gene?
It's more than likely that the cousin's get their eye color partially from Max's side. After all, Carl and Frank have to be Y/y for their kids to inherit.
Partially, of course, because their mom's have to play a role.
Sandra, Sandra's simple. She's got green eyes. So, definitely a y/y right there, makes sense she'd pass it on to Ben. Interestingly enough, her eyes seem to be a lighter, more yellow shade than his, so there's definitely no darkening genes going on with her. She still might have some serious lightening genes going on, but still I think it's likely she's a b/b. Ben would then also be b/b and y/y, with potentially some darkening genes passed down from Verdona.
Natalie, meanwhile, she has dark blue eyes again. Meaning, again, probably b/b, this time with potential darkening genes. This also means, that to pass on shit to her kids, she's likely a case of Y/y.
This means that Ben had about a 25% chance of having his eye color (Sandra was always going to pass down her side, but Carl could have passed down a brown or no-yellow gene, which would have left him with brown or blue eyes).
Gwen and Ken, meanwhile, each had a 12.5% chance (Natalie was always going to pass down a blue, but Frank could have passed on a brown, and either could have passed on a no-yellow). That they both do is a 1.5% chance.
All three cousins having their eye color is a 0.39% chance.
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On the other end, Kevin is... Well. For one thing the shade of brown of his eyes varies? In the sequels his eyes are done in black, which would tell us he's not only got a B gene but also probably some 'make shit darker' genes presenting. (Especially since, as stated before, Max and his sons have brown eyes and you can distinguish them as brown around black pupils, at least in UAF, but you can't with Kevin.) On the other hand, in OS and the Reboot his eyes are more of a standard brown.
And this wouldn't really matter as much, but Devlin exists- he may not be canonically canon to the sequels but that he exists in any timeline is enough for this- and his eyes are on the dark end. Which would mean Devlin has some 'make shit darker' genes going on, some of which he probably inherits from Kevin but we can't know how much if we don't have a shade for Kevin's eyes. He could be getting all of them or half of them, or even none they could all come from his mom's side, and yet-
But that's beside the point. We can still get the two basic genes down. Namely, Kevin is almost definitely a case of B/b. Especially if Devlin is inheriting 'make darker' genes, that blue to his eyes has to come from his being b/b. We can also safely assume that both of them have a Y, given their eyes aren't hazel or green respectively. Whether either of them carries a y though, we can't know for sure.
But we can look at the supposed family in UAF. They're not technically canon outside of UAF, but hey, they're something.
And here's an interesting one for you- Devin has the same thing going on as sequel Kevin where the eyes are so dark they're either full-on presented as black or are nearly indistinguishable from black. But his mom, has similar 'visibly brown' eyes to the Tennysons and OS/Reboot Kevin. So literally this boy could be going either way, two only fucking parental eye colors we have (we never even see his only reboot!parent's upper half) and they're 'sequel shade of brown' and 'non-sequel shade of brown'. Motherfuckers. So yeah, shit still stands until we get an actual view of some actual parents (if we ever get an actual view of some actual parents) to compare to.
Kevin is definitely B/b, could be Y/Y or Y/y we can't know, and may or may not have 'make iris darker' genes seriously going on. Devlin, meanwhile, is definitely b/b, could be Y/Y or Y/y we can't know, and seems to present 'make iris darker' genes.
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Fuck, I forgot Kenny.
Actually Kenny is relatively easy. We've been over Ben's eyes, we just need Kai's to get a look at how his shit is set up.
Which is fun in OS because her eyes are specifically a light brown there, meaning she likely has some 'make iris lighter' genes going on, and means that OS Kenny likely receives that shit from both his parents (Ben in OS also has lighter eyes, more like Sandra's are in the sequels, while he and Kai both have more medium-toned eyes otherwise and this passes on to Kenny.)
But, overall she's actually pretty easy. She's probably a B/b, given OV, though in OS especially it's possible Kenny just inherited enough 'make iris lighter' genes to get green eyes even if she's B/B. Clearly whether Ben presents them or not he can still inherit them from Sandra. What Kai definitely is is a Y/y, given her eyes aren't hazel in any series but Kenny had to inherit a second y from somewhere.
So, likely Kai is B/b and Y/y, while Kenny is b/b and y/y. But, taking OS specifically into account, there is the chance she could be B/B and Y/y, and whatever her B situation the chance that Kenny is B/b and y/y, but with enough 'make shit lighter' genes to pull him down into greens rather than hazels.
