By my count there are at least three, and possibly four, different definitions of the word 'genre' in common usage. Eighteenth century dogma that genres were pure, immiscible, and set in stone was never borne out by experience, and generic criticism looked set to die a gentle death as critics focussed on qualities not native to any given genre but potential in all of them, qualities like 'sincerity,' 'seriousness,' 'maturity,' and so on. Structuralist critics of this century revived the idea of generic criticism, though, defining genres as sets of codes embedded within a given work. If the lead character has a tragic flaw, that's a code belonging to tragedy. Note these two codes do not exclude one another.
Genres can coexist and mingle.
Their taxonomy and classification becomes some kind of intellectual sport, perhaps to the detriment of true criticism. As I understand it, this is one aspect of the argument against a biographical genre. The presence of a certain set of generic codes led people to accept It's a Good Life if You Don't Weaken as autobiography, and confuses people aware of those codes when they read Stuck Rubber Baby or For Better or For Worse . And while it may reasonably be suggested that biographical codes aren't clear enough or numerous enough to really be said to constitute a 'genre' on their own, this is debatable, and may in the end come down to an individual's taste. The line between ' trend,' 'movement,' and 'genre' is not hard and fast.