Density of SNPs in human miRNA genes. (A) SNP density in human pre-miRNAs and flanking regions. Each bar represents the average level of all human miRNAs, error bars represent the standard deviation of the mean value. MiRNA and SNP information came from mirBASE18 and dbSNP135, respectively. Figure A shows the result of all SNPs in dbSNP135. (B) Figure B only shows SNPs with a calculated MAF > 0.01 in at least one population from four (CEU, HCB, JPT, YRI).