Especially the heads of Tokugawa "gosanke" and "gosankyo" (three privileged branches of the Tokugawa family, respectively) who referred to themselves as 'TOKUGAWA' were limited to male descendants through a line of males from Ieyasu TOKUGAWA, and if the line of the Tokugawa Shogunate family failed, they played a role to provide an heir.
特に、「徳川氏」を称する徳川御三家、御三卿の当主は家康の男系男子・子孫に限られ、徳川将軍家の血筋が絶えたときには、後継ぎを出す役割を担った。