A typical RNA-seq expression profile. Blue, density plot of log-transformed FPKM values of protein coding genes, from ENCODE cell line GM12878 (left axis). Red, Gaussian fit to the right side of the main peak. Green, fraction of genes in bin (bin size = 500 genes) with an active promoter, from  (right axis). Black, fraction of genes in bin with a repressed promoter. The dashed grey line represents the level of gene expression where the fraction of active promoters is equal to the fraction of repressed promoters, and is evaluated in FPKM and as a Z-score relative to the Gaussian fit (zFPKM).