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bbygirl-aemond · 1 year

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HotD and Hair Color: A Case Study of the Strong Boys

Hello everyone! I've discussed this in the comments of my fic before, but the genetics behind Westerosi hair colors are very interesting. It also helps to explain why people in the show treated it like such a fact that Jacaerys, Lucerys, and Joffrey were not Laenor's sons. Long story short: it would be genetically impossible for them to be Laenor's, and everyone in-universe would know it even if they didn't know what genes were. I also just wanted to discuss some other things, like why Alicent's kids were blond while Harwin's kids were not. Lastly, I'll describe the genetic background Rhaenyra's baby daddy would have needed in order to successfully pass of her kids as Laenor's.

Here are my credentials: I graduated summa cum laude with a Bachelor of Science based on gene research, and am currently getting a PhD, both at institutions with a less than 7% acceptance rate who are very picky in what research they accept. My thesis directly relates to genetics, and I've spent tons of time selectively breeding mice in order to create specific genetic combinations. So please trust that I know what I'm doing when it comes to genetics! Besides, the genetics I'm about to talk about are about as basic as you can get; you all probably learned this in middle school biology.

So let's get into it! (Can you tell I'm excited to nerd out about this?)

First of all, we need to figure out which genes we're talking about here. I'm interesting mainly in comparing Alicent and Viserys's kids to Rhaenyra and Harwin's kids, as well as any children Rhaenyra and Laenor would have had if Laenor hadn't been infertile. This means that we are only interested in the genes that determine whether someone's hair color is brown or blond. Luckily for us, this is decided by a single gene: MC1R. This gene follows a dominant-recessive inheritance pattern. This means that if a person has even one copy of this gene, their hair color will always be brown. If they have no copies, their hair will be blond. We can therefore treat this case study as if the gene follows Mendelian inheritance patterns.

Also, as a primer on gene inheritance: each parent has two copies of a gene. They each pass down one of these two onto their children, so that the kids will have one gene from their mom and one gene from their dad. I'll also be using the notation "gene 1/gene 2" to describe the two genes that any one person has.

I'm going to use some Punnett squares here in a bit, so let's establish some genotypes. I'm going to use a capital "B" to refer to the MC1R gene that makes hair brown, and a lowercase "b" to refer to its absence, where hair is blond. It's typical to use a capital letter to differentiate the dominant gene from the recessive gene. So remember: in any of the situations I'm about to discuss, if there is even a single capital "B," that person will have brown hair. 100%.

First, let's talk about Rhaenyra and Harwin. Rhaenyra is blond, so she must have the "b/b" genotype: both copies of the recessive gene. Harwin is brunet, so he must have at least one copy of the dominant "B" gene. How can we figure out which other gene he has? Well, given that his kids all have brown hair, and given that House Strong is only ever mentioned as having dark hair, and given that he's descended from the First Men who usually have dark hair, it's very likely that Harwin has two copies of the "B" gene, making his genotype "B/B." When Harwin and Rhaenyra have children, this therefore results in the following Punnett Square. We can see Rhaenyra's genotype on the left, and Harwin's on top, with the four squares in the middle representing the ONLY possible genotypes of their children:

Note that all of the possibilities are the "B/b" genotype, with one copy of each type. Remember that the "B" gene is dominant, and as long as a person has one copy they will have brown hair. This explains why Lucerys, Jacaerys, and Joffrey all have brown hair. If you're interested in another example of this genetic pairing: think of the kids that Robert Baratheon ("B"/"B") and Cersei Lannister ("b"/"b") should have had together, who should have all been brunet.

Now, why is this a problem for Rhaenyra? Because the kids she would have had with Laenor should have looked very different. Let's look at what genotypes would have resulted in Rhaenyra had been able to have kids with Laenor. Remember that Rhaenyra and Laenor are both blond, so they must both have the "b/b" genotype. I know that some people were confused about this because in the book Rhaenys has dark hair, but since dark hair is a dominant trait it's impossible for it to be passed down to someone who doesn't have dark hair:

Note that all of their children only have the "b" gene. Their parents didn't have any copies of the "B" gene, so none of the kids do. All of the possible genetic combinations in this case would result in blond children. Other pairings where we see these genetic combinations include Cersei Lannister ("b"/"b") and Jaime Lannister ("b"/"b"), and Viserys Targaryen ("b"/"b") and Aemma Arryn ("b"/"b"), all of whom have exclusively blond children.

This is why it looks so bad for Rhaenyra to have dark-haired children: because it's genetically impossible for them to be Laenor's. Now Bella, you might say, people in Westeros don't know what genes are, so how would they know? Well, even if you don't know about the existence of DNA, it's a bit obvious if never in the history of humanity have two blond parents been able to have brunet kids. Rhaenyra doesn't have even a single example to point to, and neither would anyone else. At the same time, there would be countless examples of how brunet children always have at least one brunet parent. Because the genes translate into very visible traits, the sheer power of observation and statistics is enough to damn her, unfortunately.

But Bella, you might ask, why aren't Alicent's kids with Viserys all brunet, then, since she has brown hair herself? What makes Alicent different from Harwin? Or is GRRM just bad at genetics? The answer is that it's still genetically possible for a brunet to have a blond child, because you can be brunet and still have one copy of the "b" gene if your genotype is "B"/"b." And this is what I think Alicent's genotype is.

Alicent is a Hightower, and it's important to note that Hightowers are only ever described as blond by GRRM. Now, in the illustrations and in the show we see that Alicent has brown hair, but there's no actual text that confirms this. Even if she did, there remains a strong possibility that she has at least one copy of the blond "b" gene. We never see her mother in the show, but given Alicent's children we know she must have been blonde.

So what happens when Alicent ("B"/"b") has children with Viserys ("b"/"b")? The following genotypes are possible:

So it's genetically possible for their children to have either brown or blond hair. Technically, half of their kids should have one, and half of their kids should have the other. But probabilities like this are only accurate when you have really big sample sizes (think upwards of a hundred). For example, I bred two mice together recently that should have had a 50/50 split for a specific gene, but instead they had A LITTER OF NINE WHOLE MICE with just one genotype. It's really frustrating but it's very much possible. For other pairings like this, think of book Rhaenys Targaryen ("B"/"b") and Corlys Velaryon ("b"/"b"), who also have blond children because it is still possible.

Lastly, let's get into the question: who would have been a better baby daddy for Rhaenyra than Harwin? Now, this isn't from an emotional or personal standpoint, but rather from a pragmatic one. Rhaenyra's claim to the throne was already weaker than any previous heir due to her gender, and adding obvious bastards to the mix was a big mistake. Now, I fully support Rhaenyra both morally and pragmatically in going outside her marriage to Laenor. But she needed to be much smarter about it than she was. I maintain that if Rhaenyra had simply chosen a baby daddy so that her kids would physically appear to be Laenor's, and there would be no evidence, she would've gotten away with it, even if the baby daddy had blabbed to the Greens. We see in the show that royalty has the ability to squash rumors, even ones with eye witnesses, as long as there's no direct proof: think of Viserys getting away with exiling Otto for the rumor about Rhaenyra in the brothel. These people have enough political power to get away with things as long as there's no direct, physical evidence. It's also why Viserys had Rhaenyra take the moon tea, because if she'd become pregnant it would have been physical evidence that not even he could have denied.

So Rhaenyra just needs to ensure that there is no possibility of her children coming out brunette. She doesn't really have to worry about hair texture, or skin color. If her kids come out with straight hair, that's fine, because she has straight hair. If her kids come out paler than Laenor, that's fine, because she's paler than Laenor. She can pass it off as them taking more after their mother. The way she couldn't pass off Harwin's dark hair as coming from her side. So what does this mean?

TLDR: Due to genetics, Rhaenyra would have gotten away with having bastards if she had picked literally any blond man. She didn't need to pick Corlys Velaryon, which is what some people seem to think would have been her only other option. She didn't even need to pick a Velaryon. As described above, the dude didn't even need to be trustworthy. She just needed someone blond, people! Then she would have had the exact same genetic possibilities for hair color as she would have had with Laenor. All of her children would have been blond. Everyone in Westeros would understand that two blond parents would have blond children, as had always happened throughout history. And that, combined with the Velaryons' support, combined with Viserys' support, combined with Rhaenyra's own political power, would have been able to squash any rumors of bastardy. Because as the show proved, even Otto couldn't get a rumor to take off if he didn't have physical proof.

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