Kekkei Genkai

are abilities passed down genetically within specific clans. It's possible for a shinobi to have more than one of these abilities. 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, or other bodily manipulations that are usually unachievable by normal standards.

Overview
Kekkei genkai and their related techniques cannot be taught to or copied by others. However, these techniques can be given to others. Dōjutsu, or other kekkei genkai isolated to a single organ, can be transplanted into the body of another, as was done with transferring Obito's Sharingan to Kakashi. Use of these organs requires much more chakra than someone born with the kekkei genkai. Chakra elements can also be passed down to people outside of the clan, such as Yamato being subjected to DNA re-modification by Orochimaru who wanted to acquire the Wood Release kekkei genkai. However, Yamato's skill in using it is not nearly as powerful as the originator: Hashirama Senju, and the risk of such process was that Yamato was the only one of the sixty test subjects to survive. Kabuto Yakushi managed to gain access to the Kaguya clan's Shikotsumyaku and Sakon and Ukon's Kekkei Genkai by transplanting their DNA into himself, creating a clone of the original wielders connected to his own body and using the abilities through that clone. Some Tailed Beasts are also known to possess Kekkei Genkai and can pass them on to their respective Jinchūriki, examples include Shukaku's Magnet Release and Son Gokū's Lava Release.

Although kekkei genkai are usually genetically shared within a specific clan, sometimes it is unique to one person alone, and that even family relatives do not share it, such as the Wood Release and Shikotsumyaku. Yet other kekkei genkai seem to appear in individuals with no known relation, such as the Lava Release, which has appeared in ninja from Kirigakure, Iwagakure, Kumogakure and Amegakure in the anime and Magnet Release, which has appeared in ninja from both Kumogakure and Sunagakure, though these kekkei genkai are subject to variation in each village.

There is an advanced variant of kekkei genkai known as kekkei tōta, which is a combination of three different nature transformations.

List of Kekkei Genkai
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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, even dōjutsu.

Trivia

 * Kekkei genkai 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.
 * When a person is brought back to life via the Summoning: Impure World Reincarnation technique, they also retain any kekkei genkai they possessed before their death.
 * A kekkei genkai should not be confused with hiden techniques. Hiden techniques are exclusive to a certain person or clan, but only because they have kept others from learning how to perform those techniques.