Chromosomal distribution of pig OR genes. Pig OR genes were mapped to 46 regions across 16 chromosomes. The number of functional and pseudo OR genes at each cluster is indicated to the right of the chromosomes without and with parentheses, respectively. Clusters with and without functional OR genes are indicated by red and green lines, respectively. The position of each cluster is shown to the left of the chromosomes in megabases (Mb). The names of clusters indicate the chromosome number and distance (Mb) from the top of the chromosome, i.e., the cluster 10–28, positioned at 28 Mb region of chromosome 10. “U” indicates a group of sequences with no chromosome assignment in the pig genome assembly Sscrofa10.2. Chromosome figures were modified from Rothschild et al..