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Labrador genetics
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Fur Coat Color Inheritance in Labrador Retrievers
Labrador Retrievers are a popular breed of dog due to their good nature. Three principal coat colors are recognized:
Black, Chocolate and Yellow. There are two principal genes responsible for coat color in the Labrador Retriever and
both demonstrate a dominate and a recessive allele. In terms of the the pigments of this breeds fur the two alleles are
Black and Chocolate (B and b) and Black (B) is dominate. Then there is a recessive gene which can mask the ability to
express coat color. Let's call this expression gene "E" and it occurs in a dominate and recessive alleles. In order to mask
the ability to express the coat color the "E" gene must be present as homozygous ee. The presence of two recessive "e"
alleles always masks the effects of the B alleles(e.g., B or b) no matter what type of B allele (dominate or recessive) is
present. The result of the presence of two recessive "e" alleles is a yellow Labrador Retriever. Thus in order to be
guaranteed that the result of a mating of two dark Labradors will not produce any Yellow Labradors at least one of the
dogs would have to be homozygous for the "E" allele.
Fig. 1. Allele combinations which produce the three common color phases of Labrador Retrievers (Black, Chocolate
and Yellow left to right)
Work out the punnet square for possible gametes, zygotes and phenotypes for the cross depicted in the Figure 2 below.
Pairs of B and E alleles (gametes) should be filled in the four cells below the male and to the right of the female.
Possible outcomes (gamete pairings in zygotes) should be filled in the light yellow cells of the table.
Fig. 2. Punnet Square problem for a cross between two dark Labradors, one Black one Chocolate.
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12/2/2010