A 24-bp nucleotide sequence insertion was identified in the PRLpro2 PCR product, therefore, the PCR products of PRLpro2 were directly electrophoresed for 3 h at 16 V/ cm on 12% acrylamide gels for genotyping. The PCR products of each homozygote were purified using DNA Fragment Quick Purification/Recover Kit,5 and ligated to the pMD 18-T vector,5 and transformed into DH5-α Escherichia coli5 for PCR product cloning (Sambrook et al., 1989). Sequencing was performed on an ABI377 se- quencer to identify the mutation site.