Intron/exon structure and microsynteny of Daphnia and insect Halloween genes. A) Introns are mapped on the aligned protein sequences of Spo (CYP307A1), Spot (CYP307B1), Spok (CYP307A2), Phm (CYP306A1), Dib (CYP302A1), Sad (CYP315A1), Shd (CYP314A1). Introns located at the same position and in the phase (the nucleotide position of the intron within a codon: phase 0 between codons, phase 1 after the first base and phase 2 after the second base), on the aligned proteins, are shown as conserved by connecting vertical lines. Insect introns represent introns found in species of insects previously described , except Tribolium shd which exhibits unique introns that are not shown. B) Preserved microsynteny in local genome regions surrounding phm and spo(k). The arrangement of phm and its paralog CYP18A1 is conserved in insects and Daphnia and so is the microsyntenic relationship of spo (spok in Drosophila) and neverland (nvd). Nvd is believed to be involved in the conversion of cholesterol to 7-dehydrocholesterol (7dC), the step preceding the Black Box in which Spo/Spok may function [16,26]. The transcriptional direction of the genes is shown by arrowheads. The double arrowhead indicates that ApepP is in opposite orientations in Drosophila and Anopheles.