Kekkei Genkai

are abilities passed down genetically in specific clans. It's also possible for a ninja to have more than one of these abilities. Kekkei Genkai and their related techniques cannot be taught or copied by others, but it is possible to confer the ability to another person if it's localized in a particular organ like the eyes via organ transplant, such as Obito passing his Sharingan to Kakashi, although the user will use more chakra than normal. Kekkei Genkai abilities that work via the user's eye are called Dōjutsu.

Other kekkei genkai include mixing one type of elemental chakra with another, creating a new one unique to the users, which is usually impossible for normal ninja. These traits can also be passed down through people outside of the clan, such as Yamato and Danzō going through Orochimaru's DNA re-modification to acquire the Wood Release technique, though their skill with it is not nearly as powerful as the original practitioner, Hashirama Senju.

Trivia

 * Kekkei Genkais can be preserved through the creation of Human Puppets. This allows them to retain the special traits of the users when they were still alive.
 * A Kekkei Genkai should not be confused with Hiden jutsu. Hiden jutsu are exclusive to a certain person or clan, but only because they have kept others from learning how to perform those jutsu.
 * When a person is brought back to life via the Summoning: Impure World Resurrection technique, they also retain any kekkei genkai they possessed before.

Inspiration
The concept of special ninja techniques limited by bloodline inheritance may have been inspired in part by the works of Futaro Yamada, which strongly influenced later depictions of ninja in fiction. In particular,, published in 1959, featured a pair of warring ninja clans that, through selective breeding, had produced ninja with a variety of deformities, mutations, and special abilities, including even dōjutsu.