Genetics in the Lab

This is Komen, who may hold New Hampshire state records for both the fastest 5K (17:18) and the fastest unauthorized consumption of a large pizza (about 90 seconds). But more interesting to most is how he came to assume the most popular — but not the most likely– hue of America’s most popular breed.

Have you ever wondered about the inheritance of coat color in Labrador retrievers? If you’re either a Lab owner or a nerd, the answer is likely yes; if you’re both, your curiosity is assured.

The inheritance of coat color in Labs is Mendelian and controlled at two loci. One determines whether the coat will be black (B) or chocolate (b), with the allele for black dominant. Were this the only factor responsible for Labs’ color, we would expect a randomly assembled population of them to ultimately include 75% blacks and 25% chocolates. However, a second, “epistatic” gene serves as a “color-on” (E) or “color-off” (e) signal, with color dominant; all dogs that are homozygous recessive at this locus will be yellow regardless of their B/b status.


So the breakdown goes like this: If left to mate at random (and this is decidedly not the case), 3/4 of Labs would show color (i.e., black or chocolate) and 1/4 would be yellow. Of the 3/4 showing color, 3/4 of these would be black and 1/4 chocolate, so overall, (3/4)*(3/4) = 9/16 of dogs in the population would be black and (1/4)*(3/4) = 3/16 would be chocolate.

Also, without knowing anything about individual dogs’ genotypes, we see that two yellows can only breed yellow puppies, two chocolates might produce either chocolates or yellows, and blacks might produce pups of any color. Of course, a knowledgeable breeder would be able to guarantee the arrival of a given color after a number of generations through a simple enough process of manipulation.
This site gives a basic, illustrated breakdown of the predicted results of matings between all permutations of Labs; below, courtesy of, is a 4 x 4 Punnett cross between a pair of F1 (diheterozygous) dogs.


One of these days, I’m going to have three Labs, one of each flavor. I’ll name the chocolate one Ebony, the black one Tawny, and the yellow one Cocoa, ’cause I’m funny like that, and no one except for the dogs themselves will be able to keep their names straight.

4 thoughts on “Genetics in the Lab”

  1. If you get three labs, I suggest a chocolate and two yellows. Dye one of the yellows a light red. If you walk all three simultaneously, it will appear that you have somehow animated a very large carton of cosmopolitan ice cream (I’m funny like that).
    Homer says: Mmmmm ice cream dogs… slurp slurp…

  2. I think you mean Neapolitan ice cream, not Cosmopolitan ice cream. The latter consists of Astroglide, Midol, and silicone flavors. Side note — one time I won a small road race and the prize was a free day pass to a big health club. I went in and stayed for hours and used a tanning bed for the first time. I was tan at the time (this was summer in Atlanta), and I stripped down to my skivvies. Well, in short, I burned a nice swath of perviously white skin near the top and bottom of my ass. My most sensitive areas remained protected by the underpants, while the bulk of me was still tan. So I remarked to people that I looked like Neapolitan ice cream myself — chocolate torso, strawberry hemi-ass, and vanilla junk.

  3. Oh geez. I didn’t even notice the cosmo slip. I must’ve been thinking of something else. D’oh!
    I do like your description of cosmo ice cream though.

  4. I’ll name the chocolate one Ebony, the black one Tawny, and the yellow one Cocoa, ’cause I’m funny like that, and no one except for the dogs themselves will be able to keep their names straight.
    Of course, as a non-native English speaker I don’t associate any of those three words primarily with a color; no problem keeping them apart :)
    Now, if you name all three of them “dog”, but with slight differences in inflection that you and the dogs easily learn – “dog!”, “dog?” and “dog..” – you can make everybody real frustrated real quick.

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