-The elder was born with the Sage's "Eyes"..and was gifted with his power chakras and spiritual energy.
Originally Posted by The Witcher
-The younger was born with teh Sage's "Body"..and was gifted with his life force and physical energy.
as for now (according to tobi story), I'll go with the elder having rinnegan or rikudo or extended rinnegan or w/e eyes that Sage posses..not simple sharingan..
as for why their descendant turn down to be uchiha and senju, it probably the best gen just flow down and to gain superior back only "specialist" can achieve it like hashirama and madara.
tsunade might be connected to hashirama via her mother which is seems not to cling to her Senju name anymore..
what make me confius is, if both elder and younger was sage's sons, how did that sage giving them his eyes and body??eye maybe can but body??or is it simple eyes technique and body technique??
Say whatever you like but still I believe in ODAWESOME!
I still believe Gomu Gomu fruit deserve to be a Logia
Lets read VAGABOND of Inoue Takehiko (Slamdunk)