Board Thread:Naruto Discussions/@comment-24120130-20140607191120/@comment-1512913-20140701174601

Genetics don't work in Narutoverse like IRL, chakra does though. We don't know how were Hagoromo and Hamura, Ashura and Indra conceived. For all we know, they might have been made the same way as Tailed Beasts were. Kaguya and Hagoromo each took a part of their chakra and did magic.