Genre and Sub-genres.

There are often cross grens films, the main reason behind a cross genre movie is to attract and boarder the audience of the film. Wider the audience appeal! For example, a romantic film, the demography is definitely women. However, merging comedy into a romantic film will create a cross genre, 'Rom-Com' and appeal to both men and women!

" A cross-genre (or hybrid genre) is a genre in fiction that blends themes and elements from two or more different genres. "

                                                                                                                    - Wikipedia.

                                                                                     Examples of cross genre films.
The Others(2000): Psychological horror      What Happens in Vegas(2008): Rom Com   
                                                                                                                         The Green Hornet(2011): superhero action-comedy.