The coat color of Labrador Retrievers (Black, brown (chocolate), or yellow) is controlled by two different genes. The first gene controls the color of the coat, and is either B=Black or 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.

The second gene regulates whether the color pigment will actually be deposited in the hair, and is either "E" = permits pigment deposition, or "e" = prevents pigment deposition. As above, each parent provides the offspring with either an "E" gene or an "e" gene. The "E," which permits pigment, is dominant over "e," which does not permit pigment. Thus, if either gene from the parent is "E," the offspring's genetic code for coat color pigment (Black or brown) will be deposited. The possible combinations include:


EE = both parents provide the gene permitting pigment deposition


Ee = mother supplies the gene permitting deposition, father supplies the gene preventing deposition; or eE = mother supplies the gene preventing deposition, father supplies the gene permitting deposition


ee = both parents provide the gene preventing deposition

As a result, any Lab that has at least one "B" and one "E" (BBEE, BBEe, BbEE, or (BbEe) will be Black.

A Lab that has two "b's" and at least one "E" (bbEE or bbEe) will be brown.

A Lab that has two "e's," regardless of whether it has "B's" or "b's" (BBee, Bbee, or bbee) will be yellow.

See table at http://peteducation.com/article.cfm?c=2+2109&aid=2819