Figure 1

Drosophila phylogenetic tree illustrating the numbers of intron gains and losses. Pluses indicate the number of gained introns; minuses indicate the number of lost introns. Numbers at far right of the tree represent events identified in one species. Numbers at nodes represent events assumed to have occurred in ancestors. Branch lengths are drawn roughly to scale and do not indicate precise evolutionary distances. A larger phylogenetic tree drawn to scale (with the number of intron gains and losses mapped onto the tree) can be found in Additional file 1, Figure S1.