Dog Coat Color - B Locus Australian Shepherd variant (Brown)

Acronym:	B Locus, b4
Gene:	TYRP1
Mutation:	c. 555 T>G
Inheritance:	Autosomal recessive
Sample type:	CHS (Cheek Swab), WBE (Whole Blood EDTA)

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Genetics and characteristics

B locus generates a brown dog coat color, also called liver. It affects only eumelanin, causing all black colors in the coat to turn to a brownish color. It is expressed by a recessive gene, so the dog must be homozygous (genotype bb) in order to be brown. A brown puppy can have black parents, which in this case will be heterozygous (genotype Bb), where the puppy has inherited one copy of gene b from each parent. It is genetically impossible for a liver-colored dog to have any black hairs in its coat, or for a black or blue dog to have any liver in its coat. Depending on alleles in the A and K locus, brown dogs can have some red (phaeomelanin) hairs expressed. It also affects the color of the nose and eyes, making the eyes light brown or amber and the nose brown. Brown can be the whole coat, in just some parts of the coat, or in specific patterns such as solid liver, liver with white markings, piebald with roaning, liver with traditional tan markings, grizzle/agouti liver, liver merles, liver sable, liver with greying genes and red coat color dogs with a liver pigment.

Tyrosinase-related protein 1 (TYRP1) is a protein within the melanocyte that alters the color of the skin and hair of animals. This gene is referred to as the B locus and is responsible for brown versus black coat color with brown coat color inherited recessive to black. The three alleles of the Brown (B) locus are designated bs, bd, and bc, a combination of any two of which will cause brown coat color. In the Australian Shepherd and American Shepherd dog breed a novel mutation has been identified which consists of base substitution (B locus Australian Shepherd). The mutation has not been found in 30 other tested breeds. MC1R and TYRP1 comprise an example of interactive effects between loci on a single phenotypic trait: back coat color. A dog is not black unless it has a dominant allele at both MC1R and TYRP1.

 

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Results Reported As

 

 

 

 

 

 

 

 

 

 

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References:

Schmutz, S.M., Berryere, T.G., and Goldfinch, A.D. (2002). TYRP1 and MC1R genotypes and their effects on coat color in dogs. Mamm. Genome 13, 380–387.

Jancuskova T, Langevin M, Pekova S (2018): TYRP1:c.555T>G is a recurrent mutation found in Australian Shepherd and Miniature American Shepherd dogs. Animal Genetics DOI: 10.1111/age.12709