Board Thread:Theories and Speculation/@comment-5012682-20150620162706/@comment-734582-20150627123429

ScruffyC wrote: I believe affinities for chakra natures are hereditary to an extent. Well considering that we have 5 elements plus ten Kekkei Genkai, i'm pretty sure that simple systems like Aa + Bb genes won't work. I mean, you'd need five separate genes for elements alone (say, A B C D E) and then Genkai happen when you have AB BC CD DE etc. With recessive genes you can have Ab result in the "A" element. However, i'm pretty sure this isn't a foolproof system anyway, someone with a greater-than-middleschool knowledge of biology may shed more light on this.

As to the Uchiha, considering Madara's power over fire, i'm pretty sure that the whole Fire Release thing is mostly a form of tradition. Anyone can learn any Nature Release, so it's not that strange. We also don't know what the normal age is to perform this jutsu, as Itachi was a genius who was Anbu by, what, 12 or so? Judging by Naruto, having an age of say 18 at which Nature Transform is normally done isn't so strange. Though considering that there's at least some genetic element to Chakra (hence "land of fire" etc), Fire Release is a pretty safe bet for most Uchiha to have.