Kekkei Genkai (Natural Jutsu)

KEKKEI GENKAI

it's a limited blood inheritance, these physical abnormalities are inherited through by blood ties.

Sharingan
sharingan is a doujutsu (eye jutsu), and these special red-eyes were inherited exclusively by the Uchiha clan. sharingan enables the owner to copy opponent's jutsu. yet there's a higher type of sharingan i.e. Mangekyou. it can only be awakened under one condition, killing their own best friend.

Byakugan
literally means 'white eyes' (since the iris is white). though not as cool as sharingan, these eyes also have special purpose i.e. a vast distance and penetrating view (almost 360°). however these eyes could only detect chakra. every Hyuuga clan member inherits these 'lovely' eyes, for instance Neji and Hinata.

Shikotsumyaku
there's an extinct clan called Kaguya with their unique morphic bone structures. they were able to transform their bones and compress it to max density which would be equal with steel. they could pull off their bones without bleeding (kinda creep ~>,<~) too bad the last man from his clan, Kimimaro, got ill and died on Gaara's hand.