Melanocortin receptor 1 (MC1R) sequences and topological scheme of selected species: (a) Chicken (Red Jungle fowl, Gallus gallus) Acc. No. P55167-1; (b) Barn owl (Tyto alba), A0A0E3Z8U6-1; (c) Duck (Anas platyrhynchos) U3HZ58-1; and (d) Mouse (Mus musculus), Q01727-1. Sequences from www.expasy.org database. Transmembrane regions are underlined in the mouse sequence (line 4). Gray background residues (line 1 in sequences alignment and gray circles in scheme) are positions described in avian species determining the type and amount of melanin formed (see text for details). E92K replacement (black circle) causes constitutively-activated MC1R, so that dark melanin is formed even in the absence of hormone signal, MSH. Bold residues (line 4, in alignment, hatched circles in scheme) are mouse positions equivalent to those related to the RHC phenotype (red hair color) in the ortholog human protein. Surprisingly, most of these residues have not yet been reported as important in determining bird color plumage.