In Labrador Retrievers, both yellow Labs and black Labs should have black pigment and chocolate Labs should have brown. The most common places where pigmentation is visible are the nose, lips, gums, feet, tails, and the rims of the eyes. Pigment can appear black, brown, light yellow-brown, flesh colored, pink or “liver”. “Nose color fading to a lighter shade is not a fault. A thoroughly pink nose or one lacking in any pigment is a disqualification.”
A dog’s pigmentation is determined by multiple genes and it is possible for recessive genes to emerge many generations later. The pigmentation of Labradors is controlled by melanin, a pigment molecule. Melanin is controlled by the “B” locus and when its gene product is made, it is packaged into melanosomes, small organelles in each cell. Melanosomes are transferred by melanocytes into the cells that make up the structure for the eyes, hair, and skin. The color of the cells is determined by the color of the melanosome and the density of melanosomes within the cell. There are two types of melanin; Eumelanin and Pheomelanin. Eumelanin is responsible for black or brown pigment and Pheomelanin is responsible for red or yellow pigment.
Eumelanin, controlled by the B locus, is responsible for producing and packaging the melanin into the melanosome. Both the “B” and “b” alleles will produce eumelanin that contribute to pigmentation, but the dominant allele “B” is more efficient and packs more melanin into each melanosome, producing a black dog. The less efficient recessive allele “b” is responsible for chocolate coloration when the individual is homozygous recessive at the B locus.
For the purposes of illustration we will say that B=Black and b=brown. Each parent provides the offspring with either a “B” gene or a “b” gene. Black is dominant over brown. This means if either gene from the parent is “B,” the offspring’s genetic code for coat color will be Black. The genetic combinations include:
• BB = both parents provide a Black gene
• Bb = mother supplies Black, father supplies brown; or mother supplies brown, father supplies Black
• bb = both parents provide a brown gene
An offspring with one or two “B’s” will have a Black nose; one with two “b’s” would have a brown nose.
Breeding in order to correct pigmentation often lacks dependability. Because color is determined by many genes, some of which are recessive, crossbreeding a pigmentation non-standard yellow Lab to a black Lab may not correct the matter or prevent future generations carrying the same recessive genes. For similar reasons, crossbreeding chocolate to yellow is also often avoided. Fortunately, DNA color testing can be performed, which is available for around $85. This is the best way to determine the genetic combination of a dog for breeding purposes.
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