Why does kakshi have the sharigan and he isn't in the uchia clan?

Kakashi has the sharingan eye because his teammate,

Obito Uchiha, was dying, and his dying wish was that Kakashi took his sharingan eye, because Kakashi had lost his eye trying to save Rin, (his other teammate) and so, Rin put Obito's eye (don't puke) in Kakashi's empty socket.

And that is why Kakashi Hatake has a Sharingan eye, even though, he is not in the Uchiha clan.