Abstract: The numbers of mRNAs and proteins that are found in a cell are usually low, amounting to less than hundred for most types of mRNA. The statistical distributions of these among the cells of an otherwise identical population feature high variances. To understand the origins of this expression noise, we employ a combination of genomewide readout systems and experimental techniques that resolve gene expression at the single cell level. Our findings demonstrate that all genes can be separated, based on their expression abundance, into two distinct groups: one group comprised of lowly expressed and putatively non-functional mRNAs, and the other of highly expressed mRNAs with active chromatin marks at their promoters.