Board Thread:Naruto Discussions/@comment-5273810-20150830183321/@comment-3965545-20150830185633

You need the flesh, which brings the DNA, which brings the chakra.. or more simply the DNA itself which brings the chakra.. In an Uchiha's case, once the Sharingan, Rinnegan etc is awakened, they stay awakened so although they used up the chakra Hagoromo gave them in their fight, Sasuke still kept his Rinnegan... BUT Kakashi who is NOT an Uchiha was not able to keep his Mangekyo once Obito gave him his chakra.. See? If Kakashi had the KKG, the physical eyes transplanted.. or even Obito's DNA transplanted he would have kept the Sharingan eyes.