The effect of TEs on non-mammalian transcriptomes. (a) Summary of the number of exonized TEs in the different species. (i) Illustration of the exonization process, in which a TE (gray box) is inserted into an intron (line). Exonization of a TE may (ii) generate a cassette exon, (iii) create an alternative 5' splice site (Alt. 5' ss), (iv) create an alternative 3' splice site (Alt. 3' ss), or (v) be constitutively spliced (Const.). The table on the right shows the numbers of exonized TEs in each of the examined species. (b) Summary of the effect of TE insertions into the first or last exons. (i) Illustration of insertion of TEs (gray box) into an exon (white box). The insertion of the TEs may enlarge (ii) the first or (iii) the last exon.