I've asked plenty of gay guys. A large portion of my friends and my family's friends are gay. Some believe it's strictly biological and some don't. Based solely on scientific observation there is no evidence of a "gay gene". If it is in fact there, it hasn't been found yet.
The American Psychological Association had this to say (APA.org Jan 09)
"There are numerous theories about the origins of a person's sexual orientation; most scientists today agree that sexual orientation is most likely the result of a complex interaction of environmental, cognitive and biological factors. In most people, sexual orientation is shaped at an early age. There is also considerable recent evidence to suggest that biology, including genetic or inborn hormonal factors, play a significant role in a person's sexuality. In summary, it is important to recognize that there are probably many reasons for a person's sexual orientation and the reasons may be different for different people."
Just like I said earlier there are dudes that like skinny chicks and dudes that like fat chicks. Are you going to tell me there's a "fat chick gene"?