Are they? Would you elaborate on it or link some reading material? I've never heard of religion being heritary and your claim is pretty strong to just throw out there without any additional information.
[1] argues that pro-religion alleles are likely to become more common over time, since in the contemporary world religious people (on average) have more children than the non-religious
It seems unlikely there is any single "God gene". Rather, certain personality traits (such as agreeableness) increase the likelihood of a person accepting religion, and genetics contributes to those traits, which in turn indirectly contributes to religiosity