If there is a gay gene, then there is a straight gene. It is probably more than a single gene that determine who is more homosexual that heterosexual... or vis versa. And in other cases (which i think more common than the other two) there is a similarly prevalent amount of the two.
Please give me a home where cloud buffalo roam
Where the dear and the strangers can play
Where sometimes is heard a discouraging word
But the skies are not stormy all day