Systematic change in relative size of 5' IGRs of maternally expressed human and chicken one-to-one orthologs. Shown is the cumulative distribution of fold-change difference in relative 5' IGR size for all human, chicken and mouse 1:1:1 orthologs (dotted curves) versus those expressed maternally in all three organisms (solid curves). Fold change is shown on a log2 axis. A fold change of zero implies that the length of the 5' IGRs of a gene and its 1:1 ortholog ranked the same within their respective genome. Similarly, a positive fold change implies a gene's 5' IGR has expanded in relative size in human (and/or shrunk in mouse or chicken) with respect to the relative size of its ortholog's 5' IGR in mouse or chicken. The converse is implied by negative log2(fold change).