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Pokemon Gold/Silver/Crystal showed off the second official region of the Pokemon games, and introduced all sorts of new mechanics that weren't present in Red/Blue/Yellow.
One of those features is Pokemon breeding. Take two compatible Pokemons, put them in the daycare, and after a while, they'll do the nasty and you'll get an egg as a reward. Which pretty much means that G/S/C made Pokemon sex canon.
And where is the daycare located in those games?
Route 34.
