Fig. 4.—

The expanded set of Metaseiulus occidentalis Dicer-2 genes. The phylogeny of Dicer-1 and Dicer-2 genes from four distantly related arthropods (left) with five distinct copies of Dicer-2 from M. occidentalis showing the locations of shared and unique intron positions along the length of the multiple protein sequence alignment (right). Dashed vertical lines mark the positions of unambiguous shared intron positions along the length of the alignment, which are colored according to the number of genes in which they are found (5 pink, 4 purple, 3 green, 2 blue). Confidently identified unique intron positions are shown in yellow, and ambiguous (poorly aligned regions) intron positions are shown in almond. Dramatic gains and losses of introns in M. occidentalis genes have left only a single intron position in three Dicer-2 genes that is shared with any other Dicers—Dicer-2 from Drosophila melanogaster. Examining these gene structures highlights the paucity of introns in M. occidentalis genes, especially compared with the intron-rich orthologs from Ixodes scapularis and Apis mellifera. Dicer-1 and Dicer-2 genes in the phylogeny are color-matched by species, and the only node with less than 100% bootstrap support is labeled “75.” The positions of Dicer protein domains are indicated (top) as well as the relative quality of the alignment (bottom). Dashed lines for I. scapularis Dicer-2 denote missing sequence information due to gaps in the genome assembly. DIM, dicer dimerization domain; PAZ, domain named after Piwi, Argonaut and Zwille proteins.