D locus is responsible for coat colour dilution. Known mutations of the MLPH gene (melanophilin) are responsible for most cases of diluted colours. 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. It 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.
In our laboratory, we test 3 different alleles in the MLPH gene responsible for coat colour dilution:
- allele d1: is responsible for coat colour dilution in many dog breeds
- allele d2: is present in Chow-Chow, Sloughi, Thai Ridgeback and French Bulldog
- allele d3: is present in Chihuahua, Mudi, Pumi, Italian Greyhound, Pekingese, Shetland Sheepdog, Shih Tzu, Tibetan Mastiff and Yorkshire Terrier.
In some dog breeds, several different mutations can occur at the same time. The combination of two mutations (d1/d2 or d1/d3) also leads to a diluted colour of the coat.
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Genotype
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Description
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D/D:
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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 offspring will express normal undiluted coat colour.
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D/d*(d1 or d2 or d3):
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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 colour dilution and expresses normal undiluted coat colour; the offspring will have 50% possibility to inherit D allele and 50% possibility to inherit d allele.
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d*/d*(d1 or d2 or d3):
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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.
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