Board Thread:Lore Discussion/@comment-10993011-20130618024431/@comment-8248675-20130719022134

The way I see it, the first of every dynasty always was Dovakin, like Tiber Septim. St. Alesia was blessed by Akatosh and that blessing helped her to free people from Aylieds and to find the first human Empire. The fact that she was considered the first Dragonborn before Mirak, suggests that she was a Dragonborn in more then just blood, but also in soul. I don't think there is much information about Dragonborn abilities of Ramen Cyrodil, but the fact that Akaviri Dragonguard proclaimed him the Dragonborn that they were looking for for so long, suggest that he was also full Dragonborn.

From this we can conclude that all of the three dynasties were founded by true Dragonborns. Their descendants were considered Dragonborns by blood. However, weather they had the same abilities as their forefathers/mothers, still remains debatable. However, that doesn't make them any less suitable for the ruby throne. From this point of view, it's Mede family that have less legal claims then those who still have Dragonblood, or Dragonborn themselves.