Expression histograms and platform comparisons. (A) Expression histograms based on microarray data (left column) and RNA-seq results (right column). The log₂ value of the length normalized expression levels of histogram bins is plotted along the x-axis, whereas the number of genes falling into each bins is plotted along the y-axis. Thresholds for “no expression” or “marginal expression” are shown as vertical lines at either 2-fold and 4-fold above GC control probes signals (microarray) or 1-fold and 5-fold length normalized coverage (RNA-seq), respectively. Genes classed as not expressed are colored in red, marginally expressed genes in pink, and expressed as empty bars. (B) Individual gene expression levels (log₂) are shown plotted by RNA-seq (y-axis) and by microarray (x-axis) values for either FLA2 (top panel) or FLB1 (bottom panel). Genes below marginal expression levels for microarray (2-fold GC controls, Figure 5) are shown left of the red vertical line. Genes below marginal expression levels for RNA-seq (1-fold LN coverage in panel A) are shown below the green horizontal line. The increased sensitivity of RNA-seq expression values is apparent in the 2 populations of genes visible left of the red vertical line, which all represent nonexpressed genes by microarray.