Figure 1.

Previously published models of minor intron emergence. Schematics showing the three models of minor intron emergence proposed by Burge et al. (1998), including (A) the codivergence model, (B) the fission/fusion model, and (C) the parasitic invasion model. Unicellular organisms are shown by the double-bordered ovals, while regions of the genome are displayed as lines. Black lines denote intergenic regions, gray lines for ancestral introns, blue lines for major introns, and purple lines for minor introns. Boxes represent coding regions of genes, with colored boxes denoting ancestral snRNA genes (gray), major spliceosomal snRNA genes (blue), or minor spliceosome-specific snRNA genes (purple). Arrows denote the passage of time; events occurring during this period of time are noted in text under the respective arrow. Reproduced with permission from Burge et al., 1998.