Up until 10-15 years ago, I don’t think “Young Adult” was ever really a book category. I mean, we always used to call certain books “books for teens,” but that was more of descriptive term than it was an actual industry term. Now, it appears that YA is, itself, a genre, and it’s one that “supersedes” the genre it might otherwise have been classified as. For example, we have things like YA-Fantasy, YA-Adventure, YA-Contemporary, etc.
Young Adult books, as far as I’ve seen, are really only bound by one, maybe two, parameters: (1) The main characters have to be between the ages of 12 and 18, and (2) Sex scenes that occur are more implicit than descriptive. People don’t usually mention the second parameter because it seems self-evident, but it is, if we’re being strictly accurate, a requirement.
At any rate, what all this leads up to is that so long as your protagonists are between the ages of 12 and 18, your book will most likely be classified as YA, regardless of whatever else it is. It is something an editor or publishing house would want to know, and it seems to be even more important than whether your book is a mystery, romance, thriller, or dystopia from a marketing standpoint because YA has its own section in bookstores, and if a book is YA, that’s where it’ll be found.
That being said, I wouldn’t go so far as to say that your “other” genre doesn’t matter. To be sure, readers, agents, and publishers alike will still want to know if your YA novel is YA-Fantasy or YA-Romance or YA-Mystery. In that sense, maybe it’s easier to look at YA as a kind of super-genre. There are some people who might argue that because YA novels have no common themes or structure, that it really shouldn’t be considered a “genre” at all, but more of a category (non-fiction, adult-fiction, YA-fiction?) but I’m not quite so sure I agree with that. I want to delve into that idea a little more in a different post, but for now, I leave you with this infographic from teach.com that assumes YA is a super-genre and some of the ways books have been broken down within the YA umbrella. If you’re wondering what are some good YA books, this infographic has a lot of good recommendations.