Board Thread:Theories and Speculation/@comment-5012682-20150620162706/@comment-26541067-20150630065327

anyone can do any chakra nature.but each persons particular genetic makeup/chakra will make one of these natures easier to learn and use than the others.this is an affinity. family members share genes,and have similar chakra making it slightly more likely for them to have similar affinities .clans intermarry a lot, primarily to preserve these genes,thereby ensuring children carry these genes to be able to perform the clans techniques. in some cases ,such as the uchiha,the genepool becomes so small through interbreeding that its pretty much certain the offspring will have that particular 'affinity'.therefore the person ends up with their own random affinity as well as the genetically predisposed clan affinity