Lying down on the psychiatrist's couch, the young man said to the doctor, "I wanted to see you because I think I am gay."

 "Oh?" said the doctor. "And what makes you think that?"

 "Well, my grandfather was gay, and so was my father."  

 "That doesn't mean you're gay," said the psychiatrist. "We don't believe that homosexuality is hereditary."  

 "Maybe not, but my two brothers are also gay."  

 "Really?" said the doctor, intrigued.  

 "That's right. And so are my two uncles and my cousin Morris."  

 "That IS uncanny," said the psychiatrist, his interest greatly piqued. "Tell me, isn't there anyone in your family who
 has sex with women?"

 "Yes, sir," the young man said. "My sister..."