Board Thread:Theories and Speculation/@comment-5012682-20150620162706/@comment-24757127-20150620194622

Sorry if this sounds mean but to me this is an obvious answer to a dumb question. Chakra natures are NOT hereditary. Affinity is different from chakra natures. Like it was previously stated, anyone (except Lee) can learn all 5 natures BUT your chakra affinity is the easiest to learn and will be the easiest to master. Uchiha are a special case because their clan are known for fire release, probably because of Amaterasu which they exclusively can use. A black, inextinguishable fire that takes up tons of chakra and requires a Mangekyō Sharingan to use will spark someone to learn an easier, less chakra taxing fire technique. Hence why Uchiha are known fire users. That's my theory.

It's certainly plausible that the parents' chakra nature can make it easier for their children to have that affinity but it isn't 100% true. Yin & Yang natures don't really count since they are natures that are absent of elemental chakra.