Dilution Dog Coat Colour – D2
Dilution dog coat colour is controlled by genes of D locus. D locus contains a dilution gene, which is recessive, so the d gene is dilution and the D gene is non-dilution. This means that in order for the dog to be dilute it must be homozygous (dd genotype), and if it is heterozygous (Dd genotype) it will have normal, not diluted pigmentation. In several dog breeds, who have displayed diluted coat colour phenotype, have tested negative for dilution genes. This has intrigued researchers at University of Bern to identify dilution causative genes in three dog breeds: Chow chow, Sloughi,and Thai Ridgeback, named d2 gene.
The D locus dilution gene affects both eumelanin and phaeomelanin. Dilution dog coat color is characterized by a specific pigmentation phenotype. The specific pigmentation phenotype in dogs with coat colour dilution is caused by defective transport of melanosomes which leads to an accumulation of melanosomes around the melanocytes’ nuclei as well as large clumps of pigment in the hair shafts. When homozygous with a dilution gene, a black dog becomes blue and a liver dog becomes isabella. The gene affects also nose and eye colors. In blue dogs the nose will be blue pigmented and isabella dogs are slightly darker than liver. Eyes will lighten to amber.
Chow chows, soughi and Thai Ridgebacks with diluted coat colour have shown three possible genotypes: d1/d2 or d2/d2. Testing was perfomed to identify presence of d2 gene in another 417 dogs of 56 different breeds, but the gene was present in only three named breeds.
This trait is inherited as a Mendelian autosomal recessive trait. Dilution coat colour caused by d genes may be accompanied by hair loss, the so-called color dilution alopecia (CDA) or black hair follicular dysplasia (BHFD). So far, there is not enough evidence to associate d2 gene with these health conditions.
Gabor, M., Miluchova, M., Kasarda, R., Trakovicka, A., & Stanovsky, M. (2009). Genetic polymorphims of MLPH gene in Czech pointer breed.
Bauer A. et al (2018): A novel MLPH variant in dogs with coat colour dilution. Anim Genet. 49(1):94-97. doi: 10.1111/age.12632. Epub 2018 Jan 19