Spoilers ahead. Stop reading here if you don’t want to hear about how Jon Snow (née Aegon Targaryen) and his aunt Daenerys Targaryen had torrid boat sex on the Season 7 finale of Game of Thrones. People had mixed reactions to the inevitable Targaryen incest party (it’s what Targaryens do), especially since the show juxtaposed the sex scene with the scene of Bran revealing Jon’s real name, an added reminder that he’s Dany’s nephew:
Awkward. And it could get more awkward if (more like “when”) Dany gets pregnant despite her belief that she’s infertile. The Targaryens are an incestuous bunch, preferring to keep their bloodline “pure” by doing the exact opposite of what would help prevent genetic defects. Their inbreeding coefficients (the degree to which their DNA overlaps due to incest) tend to be high. Daenerys, for example, has an inbreeding coefficient of 37.5%. For comparison, here is someone with an inbreeding coefficient of 25.4%, Charles II of Spain, the profoundly disabled final member of the Spanish Hapsburgs:
All of this raises some questions. How many of the sex scenes this season were incest? (Answer: about two-thirds) How inbred would Jon and Dany’s kids be? How much DNA do the already-inbred pair share with each other? We’re asking for a friend (who knows nothing).
To get the answers, Inverse queried Dr. Jonathan Pettitt, a geneticist at the University of Aberdeen. Pettitt confirmed that Jon and Dany share between 44% and 47.5% of their DNA, meaning all that Targaryen inbreeding over generations has made them practically siblings (50% DNA overlap). Pettitt explained how inbred their kids would be:
“Jon Snow is not so inbred as Dany, so their offspring would be less inbred. The inbreeding coefficient of any child of Jon and Daenerys would have an inbreeding coefficient (calculated as half of their relationship coefficient) of 22%. So, slightly less than that of Charles II of Spain, though not by very much.”
That’s still less inbred than Joffrey, so… it could be worse? We just have to wonder how the rest of Jon’s family will react if they find out about his relationship with Dany and start doing the math.
Bran already knows the answer, but he hasn’t bothered to tell anyone yet because he’s a dick.