B Locus Australian Shepherd – Brown Coat Colour
B Locus Australian Shepherd test enables detection of b locus genes specific for Australian Shepherd and Miniature American Shepherd dog breed.
B locus generates a brown dog coat colour, also called liver. It affects only eumelanin, causing all black colours in the coat turn to a brownish colour. 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-coloured dog to have any black hairs in their 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 colour 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 colour of the skin and hair of animals. This gene is referred to as the B locus and is responsible for brown versus black coat colour with brown coat colour 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 colour.
In Australian Shepherd and American Shepherd dog breed a novel mutation has been identified which consists of base substitution (B locus Austraian 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 colour. A dog is not black unless it has a dominant allele at both MC1R and TYRP1.