Comparison of the genomic architecture. A comparison of the genomic architecture, showing the exons (on scale) and the introns (not on scale). Colored lines were added to indicate the boundaries of the exons. The asterisk marks the intron that has been conserved from plants to higher chordates, but has been lost in insects and nematodes. We have identified the intron-exon boundaries of the alpha-skeletal actin genes in several vertebrates (Homo sapiens, Mus musculus, Gallus gallus, Atractaspis microlepidota, Xenopus tropicalis, Danio rerio), chordates (Ciona savignyi, Ciona intestinalis), nematodes (Caenorhabditis elegans, Caenorhabditis briggsae), insects (Drosophila melanogaster, Drosophila pseudoobscura, Anopheles gambiae, Aedes aegypti, Culex pipiens, Apis mellifera), plants (Arabidopsis thaliana, Oryza sativa, Populus trichocarpa) and yeast (Saccharomyces cerevisia). All insects show a single exon and all vertebrates except the zebrafish (Danio rerio) show the same exon/intron boundaries as depicted for humans.