Yeah, a lot of stuff is genetics, but don't resign yourself to nature, dude. You may not have been born with a high amount of fast twitch quad muscles, but there are definitely ways to increase your quickness. There's isometric exercises you can do... special shoes that strengthen calf muscles... parachutes you can strap to your body... etc. Yeah, the parachute sounds silly but if you think about it, it's a pretty sound idea. Running with resistance.
All genetics means is that you may never be as fast as Michael Chang was, but that doesn't mean you personally can't become 10 to 15% quicker. Of course, if nothing else, vary the speed while you run. Jog at 75% for 10 minutes, than run fast for 3 minutes, then job again, then spring at 100%, etc. Also, run uphill or up stairs.
Good luck. I'm waging my own personal war against genetics.