Phylogenetic tree and intron positions of silkworm CCE genes. Asterisks in the cladogram indicate bootstrap values greater than 50%, and the nomenclatures of clades are according to Teese et al . The intron position of sequences is shown as (|) for a phase 0 intron, ([) for a phase 1 intron and (]) for a phase 2 intron. The arrow indicates the phase 0 intron at position 229 or 230, while the arrowhead shows the phase 2 intron at position 1368. The green brackets indicate the phase 1 introns at positions 792 and 861 shared among CCEs in clades 024-026 and 030, orange brackets the phase 1 intron at position 1022 shared among CCEs in clades 013 and 024-026, purple bars the phase 0 intron at position 1165 shared among CCEs in clade 030 and red brackets the phase 2 introns at position 787 and 865 shared among CCEs in clade 020.