Board Thread:Theories and Speculation/@comment-26773508-20150908113839/@comment-25122992-20150908123304

Personally I'd say Shin's Sharingan essentially became his own after transplantation/genetic modification/whatever was done to him to gain it. The reason of this can be his unique genetic makeup, which, as we know, can accept any genetic material without rejection, so when it incorporates into Shin, it in substance turns into his own genetic material. That's the way how his clones might be able to inherit his Sharingan: although he's not an Uchiha, he adopted their genetic material (namely the eyes) and during the cloning process the resulting clones also receive it from him as if it's his own.