Fig. 2. Phylogenetic relationships and exon usage among insect orders in relation to dsx evolution.

(A) A mito-nuclear phylogeny of the four orders sampled. (B) dsx gene tree based on its coding sequence. In (A) and (B), adjacent clades are colored pink and purple, and the outgroups are colored gray and black, for contrast. (C) Exon usage of dsx across insect orders. Exons are numbered arbitrarily on the basis of mRNA initiation as per scientific convention and indicate a generalized exonic organization of dsx in holometabolous insects. Order-wise exon organization of the translated product of dsx is depicted in the center with domains and sex-specific regions colored based on sequence homology. Only those exons that are translated are shown, but 5′ and 3′ untranslated exons (not shown) may have poorly understood regulatory functions. OD1 is a DM DNA-binding domain, and OD2 is a DSX dimerization domain. Exon 5a, unique to Coleoptera, is homologous to OD2.