Technical Abstract: The Mahogany locus was first characterized in 1960 as a recessive coat color mutation in linkage group V of the mouse. It was later mapped to MMU2 and renamed (ATRN) based on high homology with the attractin locus in humans. Attractin influences the balance between agonist and antagonist at receptors on melanocytes and modifies behavior and basal metabolic rate. The role of attractin as a suppressor of diet-induced obesity may portend its application as a therapeutic intervention in obesity in mammals. Furthermore, the murine ATRN locus is located in a region harboring several QTL for body weight and fatness. Thus, ATRN is an attractive candidate gene in which polymorphisms may be responsible for a percentage of genetic variation in body composition. Chromosomal mapping of the ATRN locus has only been previously reported for the mouse (MMU2, 71 cM). Thus, the current localization of ATRN in pigs and cattle provides an opportunity for further development of comparative maps. For both pigs and cattle, new breakpoints and rearrangements relative to the mouse have been identified as a result of mapping ATRN. Prediction of ATRN location in humans using comparative mapping is not conclusive. The 24-cM region surrounding ATRN on MMU2 (52 to 76 cM) harbors several genes that map to HSA2, HSA9, HSA11, HSA15, and HSA20. This comparative region is especially 'fragmented,' with at least 14 breakpoints and rearrangements existing when relating murine and human maps. However, it can be speculated that positioning of ATRN on HSA20 is more likely, given the localization of ATRN to BTA13 and SSC17 and the conservation that exists between these chromosomes and HSA20.