Chapter 448: Hexagonal Crystal

"I had noticed before that a large part of Kakashi's chakra was converging toward his left eye, which should be nurturing that Sharingan," Haruno Sakura said. "Therefore, that Sharingan must have been transplanted."

"Transplanted?" Sasuke did not understand. "My Uchiha clan has always been proud, it's simply impossible for us to transplant our Sharingan into others."

So, where did Kakashi's Sharingan come from?

"Have you asked your father if there really was no one in the clan who transplanted their Sharingan to someone outside the Uchiha clan, like to Teacher Kakashi?" Haruno Sakura asked.

"I... haven't," Sasuke answered honestly, but he believed, with the clan's pride, even if they were to dig out their own Sharingan for extraction, they would not be willing to give it to someone else.

This is the bloodline of the Uchiha clan!

Just like the Hyuga Clan members are caged birds to prevent others from stealing their Byakugan lineage.