Features of genes for different phylogenetic age groups in the mouse. A. Gene length distributions (includes exons and introns); B. ORF length distributions; C. Median number of InterPro domains per gene; D. Median exon numbers per gene; E. Median exon lengths per gene. Box-whisker plots around median values (bars) with quartile ranges and outliers as dots. Significant (p < 0.01) distribution differences were found for ps20 (marked with *) in E (t-test). Gray bars indicate phylostrata with non-randomly distributed values for each variable, based on permutations (n = 10,000) and Kolmogorov-Smirnov tests (p<0.01).