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COLOUR GENETICS - D locus

The D gene locus holds the DILUTION gene which, in its recessive form, dilutes all pigmentation made by B (whether it be black or brown). The dominant [ DD ] is full intensity with no dilution. This will allow a black dog to be black and a chocolate dog to be brown. If a dog carries one dominant and one recessive [ D d ], the dog will appear undiluted, but will carry the recessive dilution gene hidden. The [ dd ] combination is recessive, needing two copies to be expressed. When [ dd ] acts on black, it results in a light silvery blue coat colour, with lighter eyes and smoky blue nose. This colour is the one geneticists refer to as "blue". When [ dd ] acts on brown it results in a dilute chocolate, bronzy gray or Cafe-au-lait colour with yellow/amber eyes and light rosy brown pigment. In some breeds, these dilutions are called Pearl, Isabella, Lilac and Mouse. There are few dilute Havanese at this time, but they do occur. Order of dominance is [DD] > [Dd] > [dd].Dilution needs another gene to act on, in this case B so here we will look at the combinations of the two genes together.

dog displays black [D] with [ B ] - Dominant [DD] gives intense colour to coat, nose and eyes with no dilution. The dog carries one or two copies of the dominant D allele. The dog will have a black-based coat. If he carries both the dominant and recessive copies of the D allele [ D d ] then he will have a black-based coat, but carry (hidden) the allele for the dilute, blue coat.
Phenotype - dog displays black coat
Genotype - [ BB DD ] or [ BB Dd ] or [ Bb DD ] or [ Bb Dd ]

dog displays brown [D] with [ bb ] - Dominant [DD] gives intense colour to coat, nose and eyes with no dilution. The dog carries one or two copies of the dominant D allele. With [ bb ] he will have a brown-based coat. If he carries both the dominant and recessive copies of the D allele [ D d ], he will appear brown but carry (hidden) the allele for the dilute chocolate coat.
Phenotype - dog displays brown coat (chocolate)
Genotype - [ bb DD ] or [ bb Dd ]

dog displays blue [ dd ] with [ B ]: Recessive [dd] dilutes coat, leather and eyes. When it dilutes black, the dog appears silver blue. He will have self coloured pigment and lighter eyes.
Phenotype - dog displays blue coat colour
Genotype - [ BB dd ] or [ Bb dd ]

dog displays dilute chocolate[ dd ] with [bb]: Recessive [dd] dilutes coat, leather and eyes. When it dilutes brown, the dog appears dilute brown, cafe-au-lait colour. He will have self coloured rosy brown/beige pigment and lighter eyes. The dilute chocolate dog needs two copies of the recessive [ bb ] gene as well as two copies of the recessive [ dd ] gene to be expressed.
Phenotype - dog displays dilute chocolate colour
Genotype - [ bb dd ]