1. A Central American rodent of the genus Dasyprocta, related to guinea pigs.
2. A coat colour in mice in which there are alternate light and dark bands on individual hairs. The gene responsible encodes a secreted protein (131 aa) that regulates phaeomelanin synthesis in melanocytes, binds to the melanocortin receptor 1 but does not antagonize α-*melanocyte stimulating hormone, and has antiproliferative effects on melanoma cells in culture. Mice with dominant mutation at the Ay locus develop diabetes and obesity. The dark agouti (DA) rat has a high susceptibility to developing arthritis. Agouti-related peptide (AGRP, 132 aa) is a neuropeptide that increases appetite and decreases metabolism, an endogenous antagonist of melanocortin type 3 and 4 receptors. Secretion of AGRP and neuropeptide Y is stimulated when the amount of stored fat and leptin decreases. A polymorphic variant has been proposed to play a role in late-onset obesity.