Genetics in Game of Thrones: Blood on the Dragon

I think you’ll had as much fun reading these when i did writing them. This will be the final one, unless the brand new book reveals some totally wacky inheritance or even the year seriously deviates in the books. And i also’d want to speak about something that Daenerys Targaryen waxes poetic about for a long time and ages: dragons.

I’m not likely to talk of whether dragons are biologically plausible (short answer: they’re not). I’m gonna look at an element that is certain ways even less plausible: the notion that certain human families have heritable dragon-ness, presents them an affinity towards beasts as well as a certain capacity fire. That is explicitly stated of Daenerys: she can spend time within a pyre overnight and be relatively unscathed. And she can, using a degree of effort and willpower, control Drogon. Viserys says he will develop the trait but doesn’t, to horrifying repercussions. And certain other characters in later books either appear to have an affinity to dragons – but they haven’t been tested with fire at the time of yet – or think they’ll with, again, unfortunate repercussions.
Daenerys as well as a newly hatched dragon

I don’t see that much of a family resemblance, do you?

There are 2 reasons I would like to mention this trait: to begin with, it really is by all appearances incredibly rare. It appears to be for being entirely connected to 1 family, and only certain individuals within that family. Secondly, within a world with dragons, it will be incredibly advantageous. Not merely the ‘not as likely to get eaten by the dragon’ bit, which may seem to me to become entirely relevant, but also the ‘fire-proof’ bit. So since it’s so advantageous, and as there are a specific number of people in Westeros claiming Targaryen blood, why aren’t more Westerosi fire-proof?

In real life, why would an advantageous trait remain rare in a population?
Sandor Clegane (“The Hound”)

His only fear is fire. Evidence that they’s not just a dragon, I suppose.

One possibility is that it’s related to a disadvantageous trait. If that’s the case, the relative advantages and drawbacks balance one another out. The allele that produces sickle-cell anemia is definitely an obvious example of this: in heterozygotes, it will give you potential to deal with malaria (a huge advantage), as well as in homozygotes it gives you sickle cell anemia (a huge disadvantage). And those two forces balance each other out: in African populations, where malaria is endemic, the selective advantage in heterozygotes was enough to generate the allele common, nevertheless the drawback to sickle cell kept it from sweeping the people. In European populations, where malaria wasn’t as much a challenge, the bonus from the heterozygote is slowly removed and the allele is pretty rare. In Daenerys’ case, maybe her infertility is linked to her affinity with dragons. In that, case, it will be an attractive strong selective force against the allele: since good thing about not eaten by dragons will be balanced by the problem with not being able to have kids.

But that gets really hairy really fast. To begin with, it’s besides difficult for Dany to own kids: as much as she knows, it really is flat-out impossible. Knowning that trait, infertility, doesn’t often run in the Targaryen family (side note: infertility is truly one of those traits that rarely runs in families for somewhat obvious reasons). The only method this works at all for the phenotypes we’re absolutely clear on is that if it’s almost exactly like sickle cell: you will get fire-proofed with at least one copy in the dragon allele, and infertility should you have two. Which suggests both of Dany’s parents had to be carriers for that gene, along to become fire-proof (possible, they’re both Targaryen by descent). And Viserys just got unlucky: zero copies, therefore you burn off.
A chart shows differential longevity in people with different hemoglobin alleles

This chart shows longevity of individuals with assorted alleles of hemoglobin connected to sickle cell anemia. A is wild-type, S is sickle-cell. AS individuals do the top, then AA, then SS. Here, the allele is selected for to stay in a population, however , not sweep to 100%.

There’s a clear challenge with this paradigm, and it’s what I discussed around my last post: the Targaryens are notoriously inbred. Which means they’re unlikely to get particularly numerous avenues where they’re heterozygous for love or money. A solid selective force against homozygotes may lead to inbred populations retaining heterozygosity, but that could create a great deal of dead ends in the Targaryen genealogy, which might be notably absent.
The Targaryen family tree

Lots of loops, yes, and not many dead ends.

Nevertheless it seems the inbreeding which are this balancing act unlikely conserve the full analogy: the next reason why an allele which can be advantageous would stay inside a small human population are if human population is genetically isolated. Isolated by, say, only having youngsters with one’s friends and family.

Plus it similar that, as far as I will tell from brief examination, a lady of house Targaryen marrying into another house happened exactly one documented time, when Daenerys Targaryen (the namesake, not the smoothness we understand) married into House Martell, to take Dorne in to the seven kingdoms beneath the Targaryens. (There’s some chance of a Targaryen-relative marrying into house Baratheon at around the time of Aegon’s conquest likewise.) There are a few illegitimate kids of various Aegons mentioned, but a family so apparently obsessive about purity of blood because the Targaryens could, believably, have gotten relatively few bastard children. Thin trait might remain common among Targaryens and rare within the other countries in the population, simply because Targaryens only marry Targaryens.

It’ll take another book, or two, before could who, differently Daenerys and her ancestors, has enough Targaryen blood to ride a dragon. And yes it may turn out that ‘blood from the dragon’ is definitely an emergent rather than an inherited trait: which you don’t desire a genetic link to old Valyria so that you can have an affinity for fire-breathing lizards. (I’m holding out for Tyrion on the dragon, not because I think it’s particularly likely but because I’ve got a special affinity for so few, snarky people.) And possibly it’s all just magical. Which was always a risk discussing science in Westeros. Though several genealogy as George R. R. Martin has created, it’s easy – and fun – to express genetics.


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sharly's blog is a group about the intersection of art, science, biology,nature and geek culture.
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