Amber is fossilized tree sap, a type of resin that bleeds from certain trees to cover a wounded area. In the right conditions, the sap becomes hard and preserved. Occasionally, insects and other animals become trapped in this sap and are preserved in near perfect condition.
The scientists of Jurassic Park used the mosquitoes that had been preserved in amber to gain the genetic material of the mosquito’s last meal, the dinosaurs. Combining this fragmented genetic code with a frog, they were able to recreate the genetic strain.
In reality, no experimental extractions have yielded any genetic material capable of recreating anything on the scale in the world of Jurassic Park.