Evolutionary gain and loss of U1 and PAS sites. a, Average number of strong U1 sites in the first 1 kb of protein-coding genes and upstream regions. b, Average number of PAS sites in the first 1 kb downstream and upstream of coding gene TSS, respectively. c, Average number of CpG islands overlapping the first 1 kb of protein-coding genes and upstream regions. Genes are divided into 12 ordered groups by gene age. X-axis indicates the age (myr, million years) of gene groups. The number of genes in each group (from old to young): 11934, 1239, 914, 597, 876, 1195, 279, 175, 198, 315, 926, and 1143. Solid red dots and blue circles indicate sites on the sense and antisense strands, respectively.