Figure 7.

Model for the process of alternative splicing. The model describes the three different origins of pseudogenes. Non-processed pseudogenes are often found adjacent to their paralogous functional gene and retain the same exon-intron structure. Processed pseudogenes are marked by the absence of both 5' promotor sequence and introns, the presence of flanking direct repeats, and are randomly integrated into the genome. In the case of the arthropod Mhc genes, these get in the first step transcribed. In a second step, the alternative exons get spliced resulting in a certain combination of alternative exons and retaining the exon-intron structure. In the case of AeaMhc3, CpqMhc3, and CpqMhc4, these transcripts have been integrated into the genome. Normally in a third step, the introns get spliced revealing the final mRNA ready for translation. Dark grey bars represent constitutive and coloured bars alternatively spliced exons. Light grey bars represent non-coding sequence.