Do sex and comedy mix? Well, duh. (Look at “Married . . . with Children.”) But what about homosexuality and comedy? Well, yes (NBC’s hit “Will & Grace”) and no (ABC’s late “Ellen.”) Despite the plunge in the ratings after she came out in 1997 on “Ellen,” Ellen DeGeneres is said to be shaping her upcoming character on her so-far-unnamed and yet-to-be-written CBS sitcom as a lesbian. New York’s Daily News reports that the new show, proposed as a cross between the old Carol Burnett variety series and the recent HBO sitcom “The Larry Sanders Show,” has been green-lighted, to begin shooting in March, and that CBS President Les Moonves says that Ellen’s sexuality in the series has never been discussed — and is not an issue.