Examples of a trans -spliced gene and an array of tandem gene duplications. A) Schematic representation of the trans-spliced Drosophila melanogaster CG1637 gene. The three annotated isoforms A-C are shown consisting of the common 3'-terminal start exon and different groups of alternative exons. If only isoform A were known a potentially mutually exclusive exon would have been found by a search for candidates in surrounding introns (case I). However, a search for candidates of all exons in all introns reveals the two groups of homologous exons that are trans-spliced in isoform A and B (case IV). Isoform C also encodes a cluster of trans-spliced exons whose sequence is homologous to that of isoform A/B. However, the exonic sequence is interrupted at different intron positions (case III). Note, that the gene structure annotated by Flybase (shown here) is different to the published one (, supplementary Figure 3). B) Gene duplications of the Drosophila melanogaster CG14502 gene. The figure shows the tandem arrangement of the duplicated genes of the Drosophila melanogaster CG14502 gene as found by WebScipio. The parameters minimal score for exons, maximal recursion depth, search in all introns and region size were adjusted for each search. With less restrict parameters less similar exons are found.