Genomic locations of silkworm odorant-binding protein genes. 38 OBP genes are distributed across six chromosomes. Another four OBP genes (obp20, obp38, 39 and 44) are represented on chromosome 26, 16, 22 and 12, respectively. The four genes have been omitted for clarity in Figure 1. BmOBP9 and BmOBP28 are not mapped to chromosomes. The horizontal lines represent the locations of each OBP gene. Transcriptional orientations of OBP genes are indicated by (+) or (-).