Board Thread:General Discussion/@comment-26247132-20160223183610/@comment-27929993-20160314013722

Skyzy wrote: I really hope this is addressed in later episodes. Also, does the black blood "randomly" appear in Grounders? How were the Nightbloods created? Is it genetically passed on and they're all descendants of Becca? But how would that happen if they Battle Royale for the Commander slot without having children of their own to pass on the Nightblood "gene"? Did Becca use the other syringes to infect more of the population with the anti-radiation vaccine? I think that when Becca came down to earth she brought those vaccines with her and injected the grounders (all or just few of them, probably she didn't have enough for all of them). After that it was genetically passed through generations, but as you might know, not all biological and genetic characteristics of the parents are passed and/or expressed. So some of the children were born with black blood and selected as Nightbloods, and others just had normal blood and considered normal people.

We don't now if the Commanders before Lexa didn't have children, and besides that, people who doesn't have actual black blood, can still have a gene which didn't got expressed and so they have normal blood, but they can still passe that it on to their children and they can be born with that active gene and so have black blood. Not really sure if i explained very well my thoughts... But hope so!