Gay gene: A gene located on the X chromosome which was proposed to determine male homosexuality. The "gay gene" was dubbed homosexuality 1 (HMS1) and the male sexual orientation gene. It was thought to be in chromosome band Xq28. The original claim for the "gay gene" was made in 1993 by Dean H. Hamer and colleagues. There has been no independent confirmation of the existence of a "gay gene" and today there is question about its existence.