The Q-Q plots for fitting a Gamma distribution to the gene-level intron Alu densities in chromosomes-1, -19, -X and -Y. The dots represent genes. The genes in the ovals on the plots for chromosome -1 and -X are regarded as outliers and further analyzed in Additional file 2.
Zhang et al. BMC Genomics 2011 12:157 doi:10.1186/1471-2164-12-157