Mc1r

The Melanocortin-1 receptor (Mc1r) is one of the key proteins in hair colour production. When stimulated by α-Melanocyte stimulating hormone (α-MSH), it will lead to the production of dark Eumelanin. The signalling can be interrupted by Agouti signalling protein (Asip) which anatagonizes α-MSH binding and leads to the production of lighter Phaeomelanin.

Mutations of the Mc1r gene can either create a receptor that constantly signals, even when not stimulated, or can lower the receptors activity. Alleles for constantly active Mc1r are inherited dominantly and result in a black coat colour, while alleles for non-funtional Mc1r are recessive and result in a light coat colour. Red hair colour in humans is usually due to a mutated Mc1r gene.