Contrary to popular belief, intermarriage doesn’t only produce genetic disorders in the following generations; science has known for some time that it can actually provide some genetic advantages.

Intermarriage, or endogamy, remains widely practiced in societies around the world with cousins, as well as nieces and nephews with their aunts or uncles. And though endogamous couples risk a higher likelihood of their offspring suffering some diseases, inbreeding can also reduce the risk of others.

In Game of Thrones, endogamy has long been the tradition of the prior ruling Targaryen dynasty. And, at least in the television version of the story — SPOILER ALERT — Daenerys, last of the Targaryen line, may have unwittingly continued that tradition recently when she bedded Jon Snow. Neither “Dany” nor Jon yet knows they are aunt and nephew.

Crest of House Lannister of Casterly Rock

But the series’ most notable incestuous couple will always be twin brother and sister Jaime and Cersei Lannister, who produced three purebred Lannister children — Joffrey, Myrcella, and Tommen (all falsely presented as Cersei’s children with King Robert Baratheon).

Though the television series has moved ahead of the books and killed off all three Lannister children, Season 7 revealed Cersei may once again be pregnant with a possible fourth child from her brother, Jaime.

So what does our current real-world understanding of genetics predict about this potential new arrival within the Lannister brood?

According to a recent article from Genetic Literacy Project (GLP), Saudi Arabia and Qatar — where half the marriages are between first cousins — show some of the highest endogamy rates in the world:

In Qatar, for example, premarital genetic screening is mandatory for all couples. The country cites an intermarriage rate of 54 percent, up 30 percent over a generation. The genetic screens look for risks of a number of disorders including, sickle cell anemia, cystic fibrosis, spinal muscular atrophy, mental retardation, epilepsy, and Down syndrome, which can occur at rates 20 times higher than in a less endogamous population.

That won’t help Cersei and Jaime as genetic screening practices are a little behind in the medieval fantasy land of Westeros.

But lest you think little Tywin or Tywina (c’mon, we all know she’ll name the little brat after her dad) is doomed to be as sociopathic as his or her late brother Joffrey, or too sickly to ever effectively rule the throne, author and journalist Jon Entine offers some hope.

Entine says while some mutant genes are responsible for terrible, debilitating disorders like sickle-cell anemia, inflammatory bowel disease, psoriasis, Tay-Sachs disease, and certain breast cancers, they may provide some positive trade-offs. The gene for sickle cell protects against malaria, for instance. And Tay-Sachs disease might protect against tuberculosis.

Ashkenazi Jews, who practice endogamy, see higher incidences of sickle cell anemia and Tay-Sachs disease, among other things. Entine cites research into Ashkenazim that suggests another possible benefit to endogamous populations, higher IQ:

Cochran and Harpending–along with numerous other scientists–postulated that centuries of endogamy within the Ashkenazi Jewish community preserved Jewish culture but at a cost. It turns out that people who suffer from these genetically related diseases share another similarity besides their Ashkenazi ancestry–they are often of unusually high intelligence as measured by standardized IQ tests.

So Cersei and Jaime could ultimately end up producing a genius, maybe the future Mozart of The Seven Kingdoms.

Of course, he or she could also turn out to possess all of Joffrey’s sociopathy plus an unusually high IQ … which would probably be bad for everyone else in Westeros. So add that one to the list of downsides. On second thought, maybe it’s still better for everyone that this little monster shares their siblings’ fates and never lives to adulthood.