Red (ee-red)

Despite the fact that ee-red is a pretty rare colour in Border Collies, the gene itself encodes for a protein that plays a central role in coat colours of dogs. The gene encodes for a receptor (MelanoCortin 1Receptor) that controls whether the pigment cell produces pheomelanin or eumelanin.

The base functionality of the receptor is to regulate some protection mechanisms against damage from UV-light. The melanocortin hormone binds to the recpeptor and causes an increase in eumelanin production and an increase in DNA repair activity. Agouti signal peptide  (ASIP; see A-locus) prevents melanocortin from binding to the receptor and β-defensin (see K-locus) also binds strongly to the receptor but doesn't activate production of pheomelanin.

The most common mutation is a change in a single nucleotide which causes the protein to be shortened by eleven amino acids. This renders the receptor non functional. Previously this allele was labeled as e but with the discovery of other loss-of-function mutations this is now labeled as e¹.

In Australian Cattle dogs a variant (labeled as e²) was found to cause the cream coat colour. In Alaskan and Siberian Huskies a white or very pale yellow coat colour was found to be caused by another variant e³. Another variant E^G was first discoverd in Salukis and Afghan Hounds but later it was found in 26 other breeds as well. E^G causes a special grey coat and is caused by a single nucleotide mutation that results in a disrupted 2D structure of the protein. Most recently a variant 'ancient red' e^A that is also a single nucleotide mutation. The allele only results effect in combination with e^A or e^1-3. It can be described as a partially recessive allele that results in phenotypes which would normally be seen in combination with E.

A well known and more common variant is E^m. The dominant allele results in a coat where eumelanin is only shown around the muzzle. It's unclear if this changes how much the MC1R receptor is expressed in various areas or that the stability or binding capacity of the receptor changes depending on the location.

In order of dominance:

E^m : masked
E^G : grey coat with specific pattern
E : wild type, coat colour determined by other genes
e^A : 'ancient red'
e^1-3 : variants of eumelanin pigment only production

Note

Traditionally the brown coat colour was called "red" in some English speaking countries. This is confusing because the E-locus produces a red/blond coat colour. Therefore the colour produced by homozygous ee dogs is often called "ee-red" to prevent any confusion.