So for a heritable trait to be expressed do you not need it to be a dominant trait? And if the parents are heterosexual wouldn't that be their dominant trait for both?
Since some traits skip generations, I'd have to say, "Not necessarily."
No, only need for it to be a heritable trait, having certain genetic tendencies in your family tree will increase your (or your offspring's) probability of displaying the trait, but it doesn't have to be dominant to manifest itself.
Look at say ... diabetes which is highly hereditary, but it doesn't mean every diabetic individual has diabetic parents - it just means it's more likely that the disease runs somewhere in the patient's family genetic tree. Or if you ever seen two dark haired parent producing a blond haired child ...same idea.