The comparison of estimated distributions of intron Alu densities in different cancer gene classes. The proposed mixture model method was used in this analysis. The curves represent the approximated Gamma distributions of Alu density for the genes with at least one intron Alu. The column charts represent the proportions of genes without any intron Alus. WG: the entire set of multiple-exon genes in human genome. C1: the cancer genes with recessive mutations. C2: the cancer genes with mutations found in germline. C3: the cancer genes with non-translocation mutations. C4: the cancer genes with dominant mutations. C5: the cancer genes with somatic mutations. C6: the cancer genes with translocation mutations. See Figure 7, Additional files 3 and 4 for the empirical distributions of Alu densities for the above six classes C1-C6.