Genomic organization of the MHC-linked olfactory receptor (OR) genes on chromosome 6. In accordance with the agreed sequence orientation for the human genome, the orientation shown here is from telomere (left) to centromere (right). Except for the top segment, each sequence segment consists of a scale bar, a bar for CpG islands, a bar for short interspersed repeats, a bar for long interspersed repeats, a bar for Alu repeats, a bar for exons, and a bar for the sequenced clone tile path. Classification of all repeats is according to the RepeatMasker program (see Methods). Transcriptional orientations are shown by arrows under the gene names and EST-confirmed splicing in the 5′-UTRs of hs6M1-16 andhs6M1-21 is indicated by interconnecting the corresponding exons. Gene positions in the 3-Mb top segment are approximate. The duplication of a 35-kb segment containing two olfactory receptor genes is boxed grey.