D locus is responsible for coat colour dilution. Mutation of the MLPH gene (melanophilin) is responsible for most cases of diluted colours. While all mutations and genes causing colour dilution has not been discovered yet, all cases of dilution cannot be explained by genetic testing. MLPH gene encodes a protein melanophilin, a key component in the hair and skin pigment formation. A mutation in the gene causes the improper distribution of melanosomes and coat colour dilution. The mutation has an effect on the formation of black eumelanin as well as red-yellow pheomelanin, though in lesser extent. The dilution of black pigment results in blue or grey coat colour, and dilution of brown pigment results light brown or isabella. D locus is not responsible only for coat pigment dilution but also dilutes pigment of the nose, pads and eyes.
|D/D:||the dog carries two copies of the dominant D allele and expresses normal undiluted coat colour; the dog will always transfer one copy of D allele to the offspring; all of the offspring will express normal undiluted coat colour.|
|D/d:||the dog carries one copy of the dominant D allele and one copy of the recessive d allele; the dog is heterozygote/carrier of d allele for colourdilution and expresses normal undiluted coat colour; the offspring will have 50% possibility to inherit D allele and 50% possibility to inherit d allele.|
|d/d:||the dog carries two copies of the recessive d allele and expresses diluted coat colour; the dog will always transfer a copy of d allele to the offspring.|