Locus B (Brown)

traditionally called liver gene

The TYRP1  or tyrosinase- related protein is a protein that plays a role in the synthesis of the eumelanin pigment. The TYRP1-gene is directly involved in the production of brown or black eumelanin and has been identified on the dog chromosome 11.

This liver gene has two alleles:

• Allele B – controls the black colour of the coat and the nose
• Allele b – controls the brown (liver) colour of the coat and the nose

In connection with the brown colour, three variants of TYRP1-gene – bs (c.991C>T), bc (c.121T>A), bd (c.1033_1035del) have been identified.  The fourth variant baus c.555T>G.c  has only been identified in Australian Shepherds.

The dog will be brown (liver), when it has two b alleles (it does not matter which one of the two “b” variants it carries – e.g. baus/baus or bs/baus...) and obtained one b allele from each parent.

If a dog obtains a dominant wild-type B-allele from one parent and, for example, the combination bcbd from the other parent, the dog´s genotype will be B/bcbd and will be the carrier of brown (liver) colour. Without testing the parents and the offspring it is not possible to decide whether the dog carries bcbd on one allele (i.e. from one parent) or on both alleles (i.e. each parent passed on to the offspring one allele) and will have brown colour.

In Australian Shepherds, tests are to be made for all 4 alleles of locus B to determine the brown coat colour. If a dog has been already tested for three known variants bs, bc, bd, so it will be sufficient to test only the fourth baus-allele .