Four pairs of primers for PCR amplification including 5 fragments of 587-2394 bp and 8 primers for SNaPshot extension reactions were designed by Primer3 online software (v.0.4.0) (http://frodo.wi.mit.edu/primer3/) according to the reference sequences from dbSNP (http://www.ncbi.nlm.nih.gov/SNP). There were homologous sequences between FCGRs, the specificity sequences were checked with the sequence databases using BLAST (http://www.ncbi.nlm.nih.gov/blast/blast.cgi). These sequences were also verified by SNPmasker1.1 (http://bioinfo.ebc. ee/snpmasker) to make sure that the different bases were caused by SNP [49] . And each primer pair was tested for potential primer-dimer and hairpin structures using the AutoDimer software (http://www.cstl.nist.gov/biotech/strbase/ AutoDimerHomepage/AutoDimerProgramHomepage.htm). The primers used in this study were listed in Tables 3.