B Locus (B-LOCUS)
A mutation in the TYRP1 gene (B locus) is responsible for the presence of brown/chocolate/liver color in the coats, noses and foot pads in many dog breeds. This coat color can sometimes be referred to as “red” in breeds such as Doberman Pinschers and Australian Shepherds. Three separate and distinct mutations can occur in the TYRP1 gene which leads to a change in the production of the black pigment known as eumelanin. A dog can inherit any two of the three mutations which dilutes the black color pigment into a brown color within the dog’s coat, nose and foot pads. A dog must have two copies of any of the three TYRP1 recessive mutations (also represented as the “b” allele) to express brown/chocolate/liver color in their coat, nose and foot pads. It’s important to note that some breeds have additional mutations that can lead to brown/chocolate/liver coloring and these mutations have yet to be identified in breeds such as French Bulldogs. It is also important to note that any number of B Locus mutations (1, 2 or 3) may be inherited on one of the two gene copies a dog inherits. The result provided by this test is capable of determining the presence/absence of each mutation but is unable to determine if those mutations reside on the same or different gene copies. In a case where a dog possesses two or more mutations, the result is reported as “C” or “At Risk/Affected” (also represented as “bb”). Whether the mutations reside on the same or different gene copies can be determined by looking at the color of the dog’s nose and foot pads. If the mutations exist on a single gene copy, the dog will exhibit a black nose and foot pads and can be thought of as a “B” or “Carrier/Not Affected” since all mutations exist in one gene copy. If the mutations reported exist on both gene copies, the dog will exhibit brown/chocolate/liver nose and foot pads and can be thought of as a “C” or “At Risk/Affected”.
A (CLEAR/NORMAL): These dogs have two copies of the normal gene, will have a black-based coat, black nose and footpads, and will not pass the mutation to their offspring.
B (CARRIER/NOT AFFECTED): These dogs have one copy of the normal gene and one copy of the mutation associated with brown/chocolate/liver coloring. They will have a black-based coat, black nose and footpads and will, if bred, pass the mutation to 50% of its offspring, on average.
C (AT RISK/AFFECTED): These dogs have two copies of the TYRP1 mutation associated with a brown/chocolate/liver coat which can result in a brown/chocolate/liver coat coloring that varies by breed and can be referred to as “red” in breeds like Doberman Pinschers and Australian Shepherds. Some dogs that carry two copies of this mutation may not show brown/chocolate/liver coat coloring and will have black nose and foot pads. Please see test description above for more information.