Fig. 1

Classifying individual genes by expression variability across species and organs. a Genes are separated by their dynamic range of expression (across all organs or tissues in all species) into constrained or unconstrained categories. Redrawn from reference [10]. b The unconstrained genes are classified by the extent to which variation across species or across organs contributes to overall expression variation for each gene (represented as a data point). Genes for which at least 75 % of the expression could be attributed to organ or species (line with negative slope) were further divided into tissue-variable genes (TVGs, orange) and species-variable genes (SVGs, green) using a two-fold threshold for the greater contribution of organ than species for TVGs and vice versa for SVGs (lines with positive slopes). The remaining unconstrained genes were classified as “Others” (purple). Redrawn from reference [1]