ORs on chromosome 2 expressed in olfactory placode cells are similar in genomic locus but not in promoter sequence. ORs on chromosome 2 were indexed by (A) promoter sequence homology order (determined by the bottom level of the Hopach fuzzy clustering tree of pairwise distance measures generated by the wordcount method outlined in Figure S3) or (B) linear order along the chromosome. Index numbers of ORs expressed in undifferentiated OP27 cells were graphed, although expression patterns in the other three conditions were similar. After RepeatMasking, only 74 chromosome 2 promoters were long enough to be analyzed. The linear index contains 288 ORs.
