Schematic of DNA shuffling method. Parental genes are cleaved randomly using DNaseI to generate a pool of fragments. These fragments are recombined using PCR with a specialized thermocycling protocol. Fragments are denatured at high temperature, then allowed to anneal to other fragments. Some of these annealing events result in heteroduplexes of fragments from two homologous parents. Annealed 3′ ends are then extended by polymerase. After 20–50 cycles of assembly, a PCR amplification with primers is used to selectively amplify full-length sequences.