This is part of a multi-page html document by Bonnie Dalzell, © 1997

B locus

This is the locus for 'brown' dilute, also called chocolate dilute and red dilute in some breeds. The normal condition is dominant and the dilute condition is recessive. the dominant gene allows the eumelanine in the coat to be fully black. If two doses of the the recessive gene are present then eumelanin in transformed to brown without affecting pheomelanin.

This gene affect the portions of the coat that would be black as well as the color of the nose, eye rims and lips. The iris of the eyes tends to be yellow or gold in homozgous b-b dogs.

On the left is a brown dilute grade doberman or doberman cross who is b b. On the right is her undiluted litter brother who is B-? .

Both of these dogs have the A locus tan point (or bicolor) pattern = a-t ?. Tan point restricts eumelanine to the dorsal portions of the dog leaving the fur on the muzzle, cheeks, inside of the ears, eyebrows, lower legs, part of the belly, and underside of the tail to be pheomelanine. This is an excellent illustration of the limitation of the effect of brown dilution only to the black portions of the dog. Note the chocolate colored nose on the brown dog.

Brown dilute interacts with a number of other genetic colors to produce unique pale shades.

A sampling of Breeds in which b-b is common.

Labrador Retriever: (Chocolate labrador)(dilutes black to chocolate)
Doberman Pinscher: (Red Doberman)(dilutes black to chocolate)
Pharaoh Hound: (all members of the breed) main action is to turn the lips and nose red and give pale eyes.
Ibizan Hound: (all members of the breed) main action is to turn the lips and nose red and give pale eyes.
Wiemeraner -: (all members of the breed) acts in conjunction with the blue dilute gene d d to produce the unique silvery coat.
American Pit Bull Terrier
Australian Shepherd: (red and copper dogs, red merles)
Australian Cattle dog: (red and copper dogs, red merles)
Siberian Huskey: (red siberians)

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