Genomic DNA was isolated from blood samples by the phenol-chloroform method. Amplifications of fragments of the promotor of PRL and all the exons of PRLR were by PCR. Primers (Table 1) were designed according to the sequence of PRL (GenBank accession no. AB011434) and PRLR (GenBank accession no. AY237377 and AY237376) using the online primer design procedure, Primer 3.0.3 The 20-μL PCR volume included 50 ng of DNA template, 0.20 mM deoxynucleoside triphosphate, 2.5 mM MgCl2, 0.20 mM primer, and 0.5 U of Taq DNA polymerase.4 The PCR protocol was 94°C for 5 min fol- lowed by 35 cycles of 94°C for 1 min, 57°C for 1 min, and 72°C for 1 min and a final extension at 72°C for 10 min. The PCR products of PRL and PRLR were genotyped by single-stranded conformational polymorphism.