Melanistic mask

At minimum, a melanistic mask will appear on the muzzle, and may also be visible on the eartips, entire ears, or entire face. Hairs in those areas will be colored by eumelanin instead of pheomelanin pigment, making it look as though the dog has a mask on its face. Eumelanin is usually black, but may instead be liver (also known as chocolate; dark brown), blue (also known as slate; dark grey), or isabella (also known as lilac; light grey-brown); accordingly, a mask may be any of these colors. Pheomelanin occurs in shades of red ranging from ivory to mahogany, which include cream, gold, and tan. A mask is visible in conjunction with a variety of coat patterns, such as tan points and sable. Nonetheless, it may be difficult to see with certain others, such as brindle, and will not be visible on a completely eumelanic coat. Any white markings on the coat, caused by a lack of pigment, will appear to be layered over the mask and other markings. == Genetic basis ==

The melanistic mask is caused by the M264V allele (known as EM) at the melanocortin 1 receptor (MC1R) locus, also known as the extension locus. It is completely dominant to the other alleles of the gene, and causes the melanocyte-stimulating hormone to bind to and activate melanocortin 1 receptors (located on melanocytes) in the mask's area, causing those melanocytes to produce eumelanin. Although Clarence Cook Little proposed in 1957 that brindle was caused by another allele at the same locus, known as ebr, his hypothesis was refuted in a 2007 study. == Gallery ==

File:Deutscher Schäferhund- portrait.JPG|German Shepherd dog with black mask File:Whippet długowłosy głowa suki MB 01.jpg|Longhaired whippet with black mask File:French Mastiff 001.jpg|Red dogue de Bordeaux with liver mask File:AlpineMastiff0077.JPG|St. Bernard with black mask and white markings File:Kerry blue terrier pl2.jpg|Kerry blue terrier with black mask. Although the coat on the body has lightened in color in a process known as "clearing" or "greying", the mask has retained its original color. File:Vilda1.jpg|Border collie puppy with black mask, tan points, and white markings. On the front portion of the muzzle, the points on the cheeks are partially "covered up", or inhibited in expression, by the mask. ==References==