Color Genetics of Labrador Retrievers
The Labrador Retrievers is a dog that can come in one of three colors, yellow, black, or chocolate. Any other color is a disqualification. While color alone should not be a factor people specifically breed for (conformation, temperament, and genetic health are more important) color is often a concern too.
In Labrador dogs color is controlled by two genes, the one for black, B, and the one for yellow, e. How these genes interplay will determine what color the dog is and what color puppies it can produce. Note that each dog always carries 2 genes for each feature.
Yellow or Not Yellow
The genes for yellow are represented by e, or non-yellow as E. As such a yellow dog will always be ee, and a dog that is not yellow will be EE or Ee. Further more all Labrador Retrievers with ee will always be yellow, as this homozygous gene combination overrides the genes we see for black or chocolate, effectively masking them.
Black or Chocolate
In dogs black is represented on the B gene, it is dominant over chocolate, which is b. A dog that is BB, or Bb, will be black. A dog that is bb will be chocolate. In both cases this also depends on the genes for the color yellow, as we have learned the dog must also have either EE, or Ee, in order to be not yellow.
Impossible Colors From Breeding Combinations
Two yellow dogs bred together can only produce yellow dogs, a chocolate or black puppy from such a mating could not occur. If such a pup was born the breeder would have to assume the dog mated with another male.
Two chocolate dogs bred together could not produce a black dog. Again, if such a puppy was born the breeder would have to assume the dog mated with another dog.
Nose Color on Yellow Labrador Retrievers
It is possible for a yellow Lab to have either a black nose, and black pigment around its eyes, or to have a brown nose and brown pigment around its eyes. Generally the black pigmented dogs are preferred. A yellow Lab with a brown nose would have the genotype of bbee. The yellow Lab with black pigment would be BBee or Bbee.
Possible Gene Combinations for Labrador Dogs
A black Labrador Retriever could be either BBEE, BBEe, or BbEE, or BeEe.
A chocolate Labrador Retriever could be either bbEE or bbEe.
A yellow Labrador Retrievers could be BBee, Bbee, or bbee.
Each parent gives one gene from each pair and this determines what color the puppies will be. A person who is curious about the genotype of their dog can have its DNA tested or can study its pedigree, in addition to noting what color pups it has produced as the result of previous breedings and work it out from there.
If we were to breed two black Labrador retrievers together, one being BBEe, and one being BbEe we can see how it is possible to get yellow pups, although only 2 out of 8 would be yellow.