I seem to remember being taught in school that science fiction is essentially a fictional world or story based on currently known scientific fact.  For instance, if you read A Princess of Mars, you can see that the author's representation of Martian terrain and creatures are based in part on what was known of the planet at the time.  It may be known that those things aren't correct now, but it's still science fiction because it was based on what scientists knew about Mars back then.

But I'm getting away from my point, which is that science fiction isn't always about space, despite what people tend to picture when they think of the genre: Star Trek, Star Wars, The HItchhiker's Guide to the Galaxy, etc.  Some of the best science fiction is actually much more subtle than that.

For instance, Taylor Five is about a 14-year-old girl who is a clone.  This short children's or YA novel is, therefore, based on what scientists currently know about cloning.  It envisions a not-so-distant future: what the lives of the first human clones might be like, why they might have been created, etc.

Taylor and the other four human clones have been brought into a world with a lot of social unrest, a lot of political upheaval, and Taylor gets caught in the middle of it when her life as she knows it is destroyed.  She discovers, as she treks through the jungle in search of help (and when she finally finds it), that she is in fact more than just a clone: She is better, stronger, faster than regular humans, a result of an experimental drug her DNA donor took.

But the book is ultimately more than just science fiction, which I would say is a hallmark of good science fiction.  It cuts to the issue of humanity when it explores the question of what really makes a person who they are: their genes, or their experiences?