Haploview 4.0 was used to calculate the strength of linkage disequilibrium (LD, i.e. the non-random association of alleles at two or more loci) using the D′ index. Relative location of SNPs within each GAD gene and the LD plot are shown in Fig. 1 (detailed information of both D′ and r2 indexes of pair-wise SNPs for each GAD gene is listed in supplement Table 1). Haplotype blocks were defined using the default method in Haploview by Gabriel et al. (2002). In general, there was high LD within each GAD gene.
