In Isla Nublar, there were two procedures throughout the tour that guests were presented with for how the animals were created. The first was Phylogenetic Mapping, which was explained by Henry Wu as taking an unknown piece of DNA, and determining by running it through a computer where it fit into the evolutionary sequence. Thus, the Jurassic Park Scientists could try to determine what animal was going to be cloned after the DNA had been analyzed. The alternative to this procedure, was to simply grow the animal and see what it turned out to be.
Jurassic Park, Michael Crichton. Page 86.