The restriction method requires the incorporation of mutations to create unique restriction sites. In a fusion-PCR, complementary oligodeoxyribonucleotide (oligo) primers are used to generate two DNA fragments with overlapping ends in a PCR reaction. These fragments are combined in a subsequent ‘fusion’ reaction in which the overlapping ends anneal, allowing the 3′ overlap of each strand to serve as a primer for the 3′ extension of the complementary strand. The resulting fusion product is amplified further by PCR. Compared to the restriction method, the fusion-PCR strategy has the advantage that the gene fusion can be made at any position within the nucleotide sequence.