Five hundred people picked at random today from the human population would not probably represent all of human genetic diversity . . . If you're going to seed a planet for its entire future, you want to have as much genetic diversity as possible, because that diversity is your insurance policy for adaptation to new conditions
when it comes to preserving genetic variation
Except that's not the goal.
If you're talking about colonizing another star system (presumably this is way the fuck after we colonize mars, the moon, IO, Titan, Venus, Murcury, and whatever else we feel like) then little things like genetic diversity upon reaching the target are of little concern.
No, you care about GETTING THERE with enough wits about you that you can continue to function, and set up something to expand your capabilities.
The fight is not to keep the diversity we see on earth circa 2000, but rather the fight is against inbreeding from making everyone retarded to the point where they can no longer function.
Once you get there, and establish colonies, food supply, and your ecosphere can expand past the mothership, you can breed like rabbits and let nature take it's course to overcome whatever detrimental effects that being cooped up in a closed space for 30 generations might have had.
Or every generation could be a fucking clone while on the way there. Seriously, this is colonizing ANOTHER SOLAR SYSTEM. This is WAY OUT THERE. It's science fiction. Just what the hell were you planning of propelling this ship with for 30 years?
Hell, taking the long view, just spreading ANY form of sustainable life is a viable goal for this sort of project. At this scale, "humans" are transient things.