Industrialist John Hammond and his bioengineering company, InGen, have created a theme park called Jurassic Park on Isla Nublar, a tropical Costa Rican island populated with cloned dinosaurs. After one of the park workers is killed by a Velociraptor, the park's investors, represented by lawyer Donald Gennaro, insist that experts visit the park and certify it as safe. Gennaro invites mathematician Ian Malcolm, while Hammond invites paleontologist Dr. Alan Grant and paleobotanist Dr. Ellie Sattler. Upon arrival, the group is stunned to see a live Brachiosaurus.
At the visitor center, the group learns that the cloning was accomplished by extracting dinosaur DNA from mosquitoes that had been preserved in amber. DNA from frogs was used to fill in gaps in the dinosaur genomes. To prevent breeding, all the dinosaurs were made female. Malcolm scoffs at the idea of such controlled breeding, declaring it impossible. The crew witness the birth of a baby raptor and visit the raptor enclosure. Grant, Sattler, and Malcolm have reservations about the idea of resurrecting dinosaurs, but Hammond and Gennaro dismiss their fears.
The group is then joined by Hammond's grandchildren, Lex and Tim Murphy, for a tour of the park, while Hammond oversees the trip from the park's control room. The tour does not go as planned, with the dinosaurs failing to appear. The group later encounters a sick Triceratops. The tour is cut short as a tropical storm approaches Isla Nublar. Most of the park employees depart on a boat for the mainland and the visitors return to their electric tour vehicles, except Ellie, who stays with the park's veterinarian to study the Triceratops.
Jurassic Park's computer programmer, Dennis Nedry, has been bribed by Dodgson, a man involved with a corporate rival, to steal dinosaur embryos. Nedry deactivates the park's security system to gain access to the embryo storage room. Nedry stores the embryos inside a canister disguised as Barbasol shaving cream, supplied by Dodgson. Because of Nedry, the power goes out and the tour vehicles become stuck. Most of the park's electric fences are deactivated as well, allowing the Tyrannosaurus to escape and attack the tour group. Grant, Lex, and Tim escape while the Tyrannosaurus injures Malcolm and devours Gennaro. On his way to deliver the embryos to the island's docks, Nedry becomes lost in the rain, crashes his Jeep, and is killed by a Dilophosaurus.
Sattler assists the park's game warden, Robert Muldoon, in a search for survivors, but they only find an injured Malcolm before the Tyrannosaurus returns. Grant, Tim, and Lex spend the night in a tree, and befriend a Brachiosaurus. Later, they discover the broken shells of dinosaur eggs. Grant concludes that the dinosaurs have been breeding, which occurred because of their frog DNAâWest African bullfrogs can change their sex in a single-sex environment, allowing the dinosaurs to do so as well, proving Malcolm right.
Unable to decipher Nedry's code to reactivate the security system, Hammond and the park's chief engineer Ray Arnold opt to reboot the entire park's system. The group shuts down the park's grid and retreats to an emergency bunker, while Arnold heads to a maintenance shed to complete the rebooting process. When Arnold fails to return, Sattler and Muldoon head to the shed. They discover the shutdown has deactivated the remaining fences and released the raptors. Muldoon distracts the raptors while Sattler goes to turn the power back on before being attacked by a raptor and discovering Arnold's severed arm. Meanwhile, Muldoon is caught off-guard and killed by the other two raptors.
Grant, Tim and Lex reach the visitor center. Grant heads out to look for Sattler. Tim and Lex are pursued by the raptors in an industrial kitchen, but they escape and join Grant and Sattler. Lex restores full power from the control room, allowing the group to call for help. The group is cornered by the raptors, but escape when the Tyrannosaurus suddenly appears and attacks the raptors. Hammond arrives in a Jeep with Malcolm, and the entire group boards a helicopter to leave the island.

Question: How do the bio-engineers keep the dinosaurs from breeding on Jurassic Park?
Answer: They ensure that all of the cloned dinosaurs are female. 
Alternative answer: all were female