Genre and Theme
Some quick thoughts on genre and theme. The following are not (at all) meant as rules about which genres should be used to explore what thematic material. Different genres have been used to explore a wide range of themes. That said, certain genres do lend themselves to exploring certain questions, and some of those combinations are noted.
Westerns tend to explore the dichotomy between civilization (order, law and the personal limitations these often cause) on one side, and individuality (freedom, lawlesness and the violence that often results) on the other. In particular as they play out across wide geographical spaces. The fact that Westerns are rooted in these wide spaces is also why Western tropes are often transplanted into space in science fiction--certain visions of the future of space travel lend themselves to this interplay between civilization on one hand, and the lands (or in this case the space and distant planets) which are not fully under the control of that civilization on the other.
Mysteries lend themselves to questions of epistemology. Who did it? How did they do it? It isn't an accident that Umberto Eco chose a mystery to explore questions of how we know, and how we know we know, in The Name of the Rose. Of course, one of mystery's interesting sub-genres is the hard-boiled private detective. In those, "who did it" tends to wane in importance, and we often get a contemporary picaresque, in which the anti-hero detective moves through different segments of society, from high society to underworld.
Science fiction is at root an exploration of the impact of change, originally primarily scientific or technological change, on human existence. Given the speed of scientific change over the last century, the relationship between scientific change and how we live has become a fundamental aspect of human experience. Science fiction has of course expanded to look at the impact of different changes--e.g., sociological, environmental--on human existence.
Romance can point to a couple (at least) classes of fiction. There are the medieval romances about King Arthur, Roland and all those both-human-and-greater-than-human characters of legend. In those, romance tells of great deeds, those actions and events that make our heart sing. The characters have abilities that exist somewhere on that continuum between mythological and human. Now, the heir to those Arthurian legends is found in our fantasy fiction, and romance has come to mean stories of love, and more specifically drugstore paperbacks with (to the uninitiated at least) interchangeable covers and plots. I admit I don't know what's going on in the field of contemporary romance fiction. However, reading Jane Austen (and her often ironic uses of romance conventions) it's obvious there is a great tradition of fiction that focuses on the love interests of its heroine, even if current marketing of "romances" points one elsewhere.
Horror is interesting, in that it starts not with an idea (like sf with technological change, mysteries with the discovery of the perpetrator) but with an emotion: fear. And then it explores this basic (maybe most basic) emotion in all its shadings and varieties. Whereas romance is felt in the heart, horror explores those feelings that arise in our bellies when all is not right with the world. Thematically, horror lends itself to explorations of morality and justice. One sees a couple underlying worldviews appear often in horror. One might broadly be viewed as horror as morality play. In this type of horror story, the protagonist breaks some law, or transgresses some boundary, and faces the consequence. What's key is that no matter how out-of-proportion the punishment is to the transgression, there is still a transgression. There is a sense of some cosmic justice underlying the universe. Another horror worldview is that we no longer have that belief in justice to comfort us. Horror is random, and can strike anyone. In this type of story, horror is used to explore a world where "God is dead" (or, as in Lovecraft's mythos, the gods are brutally indifferent to us); where the universe is governed by chance, and we are at the mercy of horrors that strike randomly, without meaning. For a complete overview of horror and its sub-genres, my favorite book is Stephen King's Danse Macabre.
In terms of fantasy, I have no overarching theory of what theme it tends to explore. I can cobble together a functional definition of it--there are one or more self-coherent changes in the nature of reality, and unlike science fictiton, there is not attempt to position those changes as being caused by technological change, or explainable by science (even a futuristic science). However, I have no specific theory--as with the other genres above--linking fantasy with any particular thematic issues. The only thought I have is that fantasy does lend itself to the exploration of gender issues. I wouldn't say that's at the core of fantasy in the same way that I find the themes above core to certain genres. However, given fantasy's ability to explore societies structured in different ways, and it's ability to create a female protagonist free from the societal restraints of any historical society, it does provide a space in which to subvert current gender expectations, and explore other possible gender roles and arrangements.
The above aren't meant to be exhaustive. And I certainly don't mean to imply either that theme is the main thing we should look for in a story, or that theme is the best place to start when writing a story. In my experience, stories usually come out of a character, or an image, or some scene, or a pre-existing story from life or literature. However, there does come a point in revising a story where theme starts to drive the selection process. One finds out one isn't just telling a fairy tale about the troll under the bridge, who the father assures his son isn't really there, but dealing with the fact that parents must in some ways lie to their young children to provide them a necessary sense of security. And at that point, theme starts to inform the images one uses, the way one describes the characters. And it is at this point where thinking about the relationship between genre and theme can also sometimes help guide one's revisions.