Board Thread:Theories and Speculation/@comment-25645405-20150719020101/@comment-26665178-20150722191757

No he used Transcription Seal: Amastera on sasuke so that sasuke would use amastera if he ever saw tobi's sharingan. Its not itachi's amastera its sasukes.

Both of there mankyo sharingan's just happen to have the 1 ability in common(abiet there not both in same eye(left/right) via being brothers.(close genetics)