So is Madara,Obito,Itachi and Sasuke sines Both Senju and Uchiha are descendants of the First Son(Uchiha) Second Son (Senju)according to Manga Cannon.
Don't you get it? Its call genetic drifting the fatter you go away from the source the more genetic drifting occurs. Thats why Madara aded Senju DNA to Uchiha DNA, to correct the genetic drifting and reverse engineer back to the source the SO6P DNA. The First Hokage Marrying Mito Uzumaki and Having a Son who was haft Senju and Haft Uzumaki created a natural reverse engineering back to the SO6P. What could it all be? Maybe the SO6P was an Uzumaki and the one true descendant to the SO6P is Naruto Uzumaki.