Gene duplication and exon structure divergence. (A) Stacked bar chart indicating the proportions of exon divergent paralogs, nondivergent paralogs, and singletons in each species. A total of 14,671, 14,445, and 10,115 genes comprise the data sets for human, mouse, and zebrafish, respectively. (B) A model of exon structure divergence. An alternatively spliced gene prior to duplication codes for both a long and a short transcript. After duplication, the long transcript becomes fixed in one of the duplicates, while the short transcript becomes fixed in the other copy. In this way, each duplicate codes for only half of the ancestral alternative splicing repertoire. The dashed lines represent alternative splicing; solid lines, constitutive splicing events that have become fixed after duplication.
