Coat Colour in Labradors
Two sets of genes, not one, control a Lab’s coloration. One set of genes controls whether the Lab will be dark (either black or chocolate) or light (yellow). Dark is dominant over light. Thus a Lab whose genotype is EE (homozygous dominant) or Ee (heterozygous) will be dark; only Labs that are ee (homozygous recessive) can be light. The second set of genes only come into play if the Lab is dark (either EE or Ee). This set controls whether the Lab is black (the dominant trait) or chocolate (the recessive trait). Thus, a dark dog (ie. EE/Ee) that is BB (homozygous dominant) or Bb (heterozygous) will be black, while the only way a dog can be chocolate is for it to be dark (EE/Ee) AND bb (homozygous recessive). So now, the possibilities for black dogs are EEBB, EEBb, EeBB, or EeBb. The possibilities for a yellow dog are eeBB, eeBb, or eebb. And the possibilities for a chocolate dog are EEbb or Eebb. Remember that puppies will get one E/e from the dam and one from the sire, as well as one B/b from the dam and one from the sire to make up their complete “code”. If you had two parents that were both EeBb (black in appearance), you can get all three colors in the resulting litter! Furthermore, when you realize that a pair of yellows can only give their puppies the ee combination, you understand why two yellows only produce yellows. In a similar fashion, two chocolates can only bequeath bb to their puppies, so two chocolates can never produce a black puppy. The eebb is an interesting case, as this is a yellow dog with chocolate pigmentation on its nose and eyerims. A dog that is bb always has this pigmentation. Under the current standard, a yellow with chocolate pigmentation is faulted. If the Lab is mismarked, for example Black and Tan, or brindled, there are other allelles present in that dog’s makeup. If you are interested in a further discussion of these genes, do look up Clarence C. Little’s classic book, The Inheritance of Coat Color in Dogs
Traditionally, the way to determine a dog’s genetic background for color is to examine the whelping box: a dog that produces yellows and/or chocolate carries those genes. And dogs carry what their parents have; a black with one yellow or chocolate parent must carry the yellow or chocolate gene. But for those who really want to know for certain can now make use of a simple blood test to determine their dog’s genotype.
A yellow Labrador with chocolate pigmentation (eebb) is known as a Chocolate point. a Dudley refer to a Lab with absolutely no pigmentation on the nose or eye rims (all pink in color), but in actuality, this is extremely rare, and probably a genetic abnormality.
Some labs have a pinkish noes. This is called “winter nose” or “snow nose”. Many yellow Labs will have dark noses in the summer that fade somewhat in the winter and repeat the cycle the next year. It is not understood why this happens. To differentiate between Labs with faded noses and Dudleys, check the eyerims and gum tissue of the dogs. A Dudley will have only light pink or tan skin; the other dogs will have black pigment in these areas.
The following table illustrates the possible combinations of alleles associated with each of the three coat colour phenotypes observed in Labradors.
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PHENOTYPE |
E |
B |
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or
or
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or
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or
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or
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COAT COLOUR IN LABRADORS
Only three coat colours are recognised in labradors: black, chocolate and yellow. Although slight variations in coat shading are conferred by a number of genes, distinction between these three main colour groups are encoded by only two loci.
One of two alleles can be expressed at the E locus: E (big E) and e (little E). A single copy of the E allele prevents the expression of a yellow coat colour. Dogs that express one or two copies of the E allele at the E locus are black or brown; the E allele is dominant. Dogs that express two copies of the e allele at the E locus are yellow; the e allele is recessive.
One of two alleles can be expressed at the B locus: B (big B) and b (little B). Providing a dog is not homozygous e at the E locus, dogs that express one or two copies of the B allele at the B locus are black; the B allele is dominant. Providing a dog is not homozygous e at the E locus, dogs that express two copies of the b allele at the B locus are chocolate; the b allele is recessive.
PLEASE NOTE: Silver or Platinum Labradors are cross breed and not correct as the Labrador has only 3 recognized coat colours = Black/Chocolate /Yellow