Figure 1. Schematic Representation of Homologous Recombination Assay. The lacZα coding region of the positive control plasmid was mutated and two plasmids with different mutations were generated. Therefore, the two plasmids containing different defective lacZα cassettes can form a functional lacZα cassette through intermolecular homologous recombination. The two defective plasmids, once transformed into bacterial cells, will form white colonies.  Only the plasmid that has undergone homologous recombination and generated the functional lacZα can form blue colonies. The homologous recombination efficiencies can be determined by calculating the percentages of the blue colonies among all the blue and white colonies.