Board Thread:Character Discussion/@comment-28282242-20160423112213/@comment-27819070-20170423013641

I think all or at least most night bloods are (distantly) related. Becca injected herself (and possibly a few others) to become a night blood, and this trait appears to be genetic, as Ontari referred to herself as "heir to Becca Pramheda", implying she is descended from Becca. Nightblood appears to be a recessive genetic trait, as many of those born night bloods are born to normal parents (likely meaning one of their grandparents other great grandparents had nightblood). Becca is clearly common heritage between all clans, as she is seemingly revered by all 12. Becca (and perhaps a few others) passing nightblood down genetically would be the only way to keep it in the gene pool. I assume that Lexa and Luna are related, but probably only as incredibly distant cousin's or something of the like. Support for nightblood being genetic is also found in Lunas noting that her brother also had nightblood, which would be bizarre if it were just a random mutation.

But then again... the most I've studied of genetics was high school science classes :)