Submitted by Reproductive Coordinator Heather Power and Breeding Program Manager Marina Hall Phillips
Talk about a sweet phone call: "There's chocolate in the whelping kennel!" announced a member of our Kennel staff. Thinking that some generous soul had stopped by with a box of See’s Candies, our initial sugar thrill turned to genuine excitement and curiosity when it became clear that the chocolate in question was referring to the coat color of some new puppies!
A maiden brood, black Lab Arizona, delivered a litter sired by a relatively new stud dog, yellow Lab Forte, on June 8. She brought a healthy litter of seven puppies into the world: five are black and two are chocolate. It is rare to see chocolate-colored dogs in GDB's colony - the last time a chocolate-colored pup was born to yellow or black Lab parents was in 1994. Prior to that, we did have some chocolate puppies produced by chocolate parents. The last active chocolate-colored breeding stock dog was a brood named Darlin, who was born in 1978. In addition, GDB has included chocolate-colored Labradors in our program obtained from outside sources through the years. To date we have had 51 chocolate dogs in our program, 13 of which went on to become working guides or breeder dogs.
As you know, Guide Dogs’ directive is to make breeding selections based on the highest potential that the resulting offspring will succeed as working Guide Dogs. GDB has developed a colony that supports our ability to meet our client demand with specifically selected combinations of black and yellow Labradors (and, if you've seen our colony, you know that the variations among the "yellow" Labs are still pretty vast!).
So how did these two chocolate treats come to be? Here's a quick and simplified lesson in genetics that should shed a little light on the subject:
There are spots on the canine genes called “loci” (or “locus” for a single spot) that deal with different coat colors. There are thousands of these loci, and it gets pretty complicated really quickly. Fortunately for us, in Labradors we really only need to focus on two loci to determine whether a dog will be black, chocolate, or yellow: B and E.
B comes in two varieties: black and brown. Black (B) is dominant, brown (b) is recessive, and the color applies not only to the dog’s fur, but to some extent all of the areas of pigment we see: nose, lips, foot pads, and around the eyes. If the dog in question has even one copy of the dominant (B) gene, s/he will have a black coat and black nose, etc. Only if the dog has two copies of the recessive gene (b) will their coat and nose look brown.
The Forte x Arizona litter's two chocolate pups are b/b on that locus. Their black littermates, however, are either B/B or B/b.
So where do yellow Labradors fit in? For them, we need to go to a different locus: E, which works a little differently. In recessive form (e), it suppresses or prevents the coat color of the B locus from expressing itself. In other words, the black or chocolate color won’t show up in the fur if the dog is carrying e/e. Instead, their coats will be yellow. Recessive (e) doesn’t remove the other areas of pigment however – they should have black noses, or at least a black rim around their noses, if they have B/B or B/b on that first locus. If they have b/b on that first locus, then those other areas of pigment will be liver colored. Couple that with e/e for recessive yellow coat color and we see a yellow coated dog with liver b/b pigment.
In a way, the coat colors are like a ladder. The first rung (or loci) tells you if the dog is black or brown, then the 2nd rung takes that black or brown dog and if double recessive, turns its fur yellow.
Phew! That's your science lesson for the day.
As for this Forte x Arizona litter, we are employing color genotype testing to identify which puppies in this and future litters carry the color genes for chocolate. The test is a simple, non-invasive DNA cheek swab. We will use this information to guide mate selection for color in the future. It's likely that we will not intentionally mate chocolate color carriers with yellow dogs who also carry for chocolate, since our focus is on black and yellow Labs. So while it is unlikely, it is certainly possible that we may see more chocolate-coated Labs in the future (if mate selection factors indicate that an ideal match would be between two parents carrying for the chocolate color). If so, we will embrace the little chocolate kisses with open arms, just as we've done with these two newest pups. The pups are thriving and will enter their puppy raising homes in just a few weeks. We're hoping we have some chocolate Lab Guide Dogs in our future!