Dog Coat Color – EG Locus (Grizzle)

Acronym:	EG Locus
Gene:	MC1R
Mutation:	c.233G>T
Inheritance:	Complex
Sample type:	CHS (Cheek Swab), WBE (Whole Blood EDTA)

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Genetics and characteristics

Grizzle coat color, also known as domino, is a coat pattern that is a mix of eumelanin and pheomelanin. This phenotype is caused by the Eg gene on the E locus, also called Extension. Whether it is called domino or grizzle depends on the dog breed in which it occurs. Like that, this phenotype is Saluki dog breed is known as grizzle, but it is called domino in the Afghan Hound breed. The name was derived from a famous Afghan Hound show dog named Tanjored Domino, born in 1954. He gained his popularity in show circles in United Stated due to his rare coat color pattern at the time. Prior to Tanjore Domino’s popularity, the pattern was called reverse mask by fanciers of Afghan Hounds.

Malamutes and Siberia Huskies are considered to be old breeds relatively closely related to the Afghan Hound and Saluki, and a similar facial pattern can be found in them. However, neither in Malamutes nor in Siberian Huskies the same causative mutation as in Afghan Hound and Saluki can be found. E locus is responsible for almost all non-agouti eumelanin or phaeomelanin patterning in dogs. E stands for ”extension”. Alleles in the E series are Em (masked), Eg (grizzle/domino), E (normal extension-has no effect on phenotype), and e (recessive red). The dominance hierarchy is the following: Em> Eg>E>e.

Grizzle coat color appears as mixed hair on the dog with no discernible pattern. The colors appear as blended together, so when until it is not examined closes, it looks like just one color. Grizzle coloring includes different coat colors, so black hairs may be mixed with some tan or brown hairs, or white with black, which results in looking as grey coat color. Official grizzle definition given by Casey and Margot is: ”A pattern that is present at birth and remains throughout life, which comprises a dark overlay covering the top and sides of the body and outside of the limbs, from the top of the head to the tip of the tail. The darker color on the head gives the impression of a ‘widow’s peak’ between the eyes which contrasts with the lighter color of the face. The underside of the dog and inside the legs comprises the lighter base color. The overlay color may be Black, Grey/Silver, red, or Chocolate and can vary in intensity with the seasons and age. The base color may be various shades of red, fawn, golden, cream, or silver.”

Eg the gene (grizzle) is dominant over all alleles of the E locus except Em (eumelanistic mask), which means a grizzle dog can never have a mask. For example, a heterozygous dog with EmEg genotype will have a mask but would not show a grizzle pattern. Also, the expression of the grizzle pattern depends on alleles of the A locus. In order for a dog to be a grizzle, except having grizzle alleles, a dog has to have tan point alleles on A locus (atat). Dog carrying Eg gene but no tan points will not be grizzle and its A locus will be expressed normally. In other words, a dog can be a carrier of the grizzle gene but will never have it expressed due to genes of its A locus.

Grizzle coat pattern is caused by a point mutation within the MC1R gene (Melanocortin 1 Receptor), which is also known as Extension (E locus). Its mode of inheritance is considered complex. The mutation appears to affect the binding of ASIP (Agouti Signaling Peptide) to MC1R which results in eumelanin hairs with phaeomelanin pigmented portions.

 

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Results Reported As

 

 

 

 

 

 

 

 

 

 

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References:

Dreger, D. L, Schmutz, S. M. (2010): A New Mutation in MC1R Explains a Coat Color Phenotype in 2 ‘‘Old’’ Breeds: Saluki and Afghan Hound. Journal of Heredity 2010:101(5):644–649.