Genetic basis of B Locus - corresponds to the TYRP1 gene, which controls the production of eumelanin pigment responsible for black or brown coloration in dogs. In Lancashire Heelers, a specific variant of TYRP1 known as Bl (or be in some sources) causes a brown (liver) coat color phenotype due to a mutation that produces a dysfunctional TYRP1 protein. This mutation is a single nucleotide change that disrupts normal eumelanin synthesis, shifting black pigment to brown in hair, nose, and footpads. The inheritance of the brown coat color at TYRP1 is autosomal recessive: dogs must carry two copies of the Bl variant (homozygous) to express the brown coat color, while carriers with one copy appear black but can pass the brown allele to offspring.
Pathophysiology - The mutation in TYRP1 impairs the enzyme’s role in eumelanin production, resulting in a brown or liver-colored coat instead of black. The brown pigment affects not only the coat but also nose and paw pad color. The variant specifically affects eumelanin pigment synthesis and does not alter phaeomelanin (red/yellow) pigmentation.
Complications - This is a color variation only and does not cause health problems. Brown coat color may vary slightly in shade depending on other coat color genes but is purely cosmetic.
Why This Matters to Breeders and Vets - Knowing the presence of the Bl allele allows breeders to predict and select coat color outcomes more accurately in Lancashire Heelers. Genetic testing aids in avoiding unexpected brown puppies or managing brown coat color as a desired trait. For veterinarians, understanding breed-specific color genetics helps in advising owners and breeders.
Summary - The Bl allele at the TYRP1 gene in Lancashire Heelers causes a recessive brown (liver) coat color through disruption of eumelanin pigmentation. Dogs require two copies of this allele to express brown coloration. Genetic testing is essential to identify carriers and affected dogs to manage coat color outcomes effectively within breeding programs for this breed.