Board Thread:Lore Discussion/@comment-92.251.228.132-20141108020915/@comment-107.178.39.95-20150405162106

You're correct. Being Dragonborn is not hereditary: not all Dragonborn are Septims, and not all Septims are Dragonborn. Only those who needed to be Dragonborn to ascend the Ruby Throne were gifted the dragonblood, and that's not even relevant anymore: the LDB doessn't have a strong claim, and even so Mede had heirs.