How can a behavior be a phenotype?

If a behavior is a phenotype, then wouldn't that also mean that there is a genotype for the behavior? If there is a genotype for that behavior then wouldn't that also mean that a allele is present on either or both chromosome inherited by the parents. Is there such a thing as a behavior allele? How can one tell the difference between what is the factoring result of mental characteristic, and the result of a genetics?