Part II. Other Genes.

Chocolate — B gene

This gene (Tyrosinase Related Protein 1) has a lightening effect on eumelanin only. I.e, it has no effect on red (yellow)-based colours.

In the dog there are two alleles for this gene, with symbols B and b respectively. When B is present (BB or Bb) the brown/black eumelanin is its normal, unlightened, colour. But when a dog is bb the brown is lightened to Chocolate.

The gene apparently codes for one of the proteins that makes up the eumelanin pigment granule, so the bb granules are smaller and rounder in shape as well as appearing a lighter colour than those of a dog carrying B. It has some effect on the iris of the eye and on the skin colour, including the eye rims and the nose leather.

Brown pumi puppies, genotype bb,E-,K-.

Blue Dilution — D gene

This recessive gene has a diluting effect on both eumelanin and phaeomelanin. When present in the homozygous recessive form (dd) it dilutes black/brown eumelanin to blue, and red/yellow to cream. This dilution is present from birth.

It is thought to act by causing the clumping of pigment granules in the hair. Like B, it often affects skin and eye colour, and in some breeds dd has been associated with skin problems and hair loss. The hair loss and skin problems which occurs in blue dogs is called «Black Hair Follicular Dysplasia» in some breeds and «Color Dilution Alopeicia» in others.

Black-born and grey-born (blue, genotype dd,E-,K-) pumi puppies.

Albino — C gene

This gene affects the intensity of melanin production in the coat hairs. The normal or dominant form, C, is what might be termed «full colour». There are however various incompletely dominant mutant alleles postulated for this locus, with varying effects on colour intensity. These mutant forms are temperature sensitive — the higher the temperature, the more effective they are (i.e, the lighter the colour).

Almost all dogs are CC at this locus - full colour. The lower series alleles that have been suggested include, in order of decreasing dominance, cch, ce, cb and c.

The first, cch, is chinchilla. This lightens most or all of the phaemelanin with little or no effect on eumelanin. E.g. it turns black&tan to black&silver.

Black-and-silver coloured Pumi, genotype: atat,cch-,kk.

Red/Yellow colour, modified by chinchilla gene: Ay-,cch-,kk and -,B-,cch-,D-,ee.

The next allele, ce, is «extreme dilution». Causes tan to become almost white. It is thought that the some of white Pumis may be cece. The ce allele may be responsible for producing white hair in Pumi with full expression of dark nose and eye pigment.

Ivory-White Colour with Dark Skin and Eyes Pigmentation
Genotype: Double silver-factored cch-,G- or extreme-diluted yellow ce-

Snow-White (Gyöngy-fehér) Colour with Dark Skin and Eyes Pigmentation
Ideal genotype: -,B-,cece,D-,ee,GG

Moving on down we have cb, or blue-eyed albino. This is an entirely white coat but with a very small amount of residual pigment in the eyes, giving pale blue eyes.

Finally we have c, true pink-eyed albino. This doesn't seem to occur in dogs.

Merle — M gene

This is an incomplete dominant that causes «merling» — patchy dilution e.g. black becoming patched with grey («blue merled») or sable becoming sable merle. Merling has little or no effect on phaeomelanin. The M allele is not found in all breeds; in fact most (include Pumi) don't have it. Merling also affects the eye colour.

Most merled dogs are actually the heterozygote, Mm. There is good reason for this; there are serious health problems associated with the homoygote MM, including tiny eyes (microopthalmic) or even entirely missing eyes (anopthamlic). The homozygote is also known as a «double merle». They are often predominantly white, hence their alternate name «defective white».

Super-Extension — Se gene

This dominant gene controls the expression of a black mask.

Traditional models of dog colour genetics placed black mask in the Extension (E) series. However it seems that a more accurate model is to place it at a separate locus. Alternate literature has used the symbol Se for this.

Most breeds do not exhibit black mask, and are therefore sese for this locus. Breeds that have black mask (Se-) include the Puli, Mastiff, Pug and Belgian sheepdog. A Pumi with mask is very rare.

White Spotting — S gene

The piebalding or «white spotting» gene is common to many mammals and it is not really fully understood.

In dogs it is thought there are four alleles, in decreasing order of dominance: S, si, sp and sw. The S series alleles appear to be incompletely dominant, further complicating matters. E.g. Ssw will be similar to sisi in appearance. The degree of white spotting is also affected by modifiers. E.g when merle (M) is also present, the white spotting has a greater effect (more white).

The most dominant allele, S, means «solid colour». Most dogs that are homozygous for S (i.e. SS) have no white hair at all, or possible a tiny amount e.g. a white tail tip, though this can be considered a fault in breeds that are normally SS.

The next allele, si, mean «irish spotting». This involves white spotting on most parts of the coat, but not crossing the back.

Moving on down we next come to sp, «piebald». The white is more extensive than irish spotting, and often crosses the back.

The most recessive allele in the series is sw, or «extreme white piebald». A dog that is homozygous for sw will be almost entirely white.

Ticked — T gene

This dominant mutation causes the presence of colour in those areas that have been made white by the effect of alleles in the white spotting (S) series. An extreme example of ticking is the Dalmatian.


2003—2007 © Länger Tamara
© Photos courtesy of Olajos Andrea, Dogheart, Nagy György, Lena Johansson, dr.Lévai Piroska, ALEX, Keve Gábor, Jade Lastikka, Eija Puhakka, Holdampf Dóra, Jona Laitinen


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