Genetics of Coat Color in Labrador Retrievers

Well, that’s where genetics comes in. But before we get into all of that, did you know Labs come in 4 colors? Yep, and I’m not talking about the “designer” dogs in silver or polar bear white. You’ve probably even seen all 4 colors and didn’t realize it.

So what are they? Well, there’s black. No surprise there. There’s also chocolate. Again, no surprise. Then we get to the yellow. Yellow has a “yellow” coat –with shades from pale cream to rich fox red—but they also have a black nose and eye rims. The fourth color looks like a yellow at first glance, but they have a chocolate nose and eye rims. These are called Dudleys and they carry the genes for both chocolate and yellow.

Back to genetics: The blueprint of each dog is contained in its DNA which is made up of 39 pairs of chromosomes. Half of those chromosomes came from the dog’s father and the other half came from the dog’s mother. Along those chromosomes are genes. Each pair of genes controls a portion of the blueprint. The corresponding genes can be the same (“homozygous”) or they can be different (“heterozygous”). If they are different, the dominant gene will show and the recessive gene will be hidden.

Okay, so that was a rather simplified version of genetics, now we can get into colors. In Labs, the gene for black (“B”) is dominant to chocolate (“b”). The “B” or “b” shows that these are two versions of the same gene and that the one with the capital letter is dominant to the small letter.

Yellow is determined by a different gene. This gene determines whether the dog will be yellow or not yellow. If the dog has one or two copies of the “E” version of the gene, it will be black or chocolate depending on the “B” gene. If the dog has two copies of the “e” version it will be yellow.

Dogs who have two copies of the “b” version and two copies of the “e” version will be yellow with a chocolate nose and eye rims.

Dogs need at least one copy of the “B” gene to have black pigment. If they also have at least one copy of the “E” gene, they will be black. If the dog has two copies of the “b” gene they will have chocolate pigment—coat if the dog also has at least one copy of the “E” gene. If the dog has two copies of the “e” gene they will be yellow and will have a black nose and eye rims if they also have at least one copy of the “B” gene.

Clear as mud? Here’s a chart:

EEBB =Basic Black (BB)

EEBb =Black that carries Chocolate (Bc)

EeBB =Black that carries Yellow(By)

EeBb =Black that carries Yellow and chocolate (Byc)

EEbb =Chocolate (C) that does not carry yellow

Eebb =Chocolate that carries yellow (Cy)

eeBB =Yellow (Y) that does not carry chocolate (black pigment)

eeBb =Yellow that carries Chocolate (Yc) (black pigment)

eebb =Yellow with chocolate pigment

So those 4 colors that we can see actually break down into 9 different colors when we look at the genetics. By the way, the letters in the parentheses are breeders’ shorthand. For example, a black that carries chocolate is a Bc.

Now let’s try combining the genes. For the sake of clarity we’ll start with just the black/chocolate gene. If both parents are black, but carry the gene for chocolate their code is Bb.

To read the chart, the father’s contribution is along the top and the mother’s contribution is along the side. In this case the genes have a 25% chance of combining as “BB”, a 50% chance of combining as “Bb” and a 25% chance of combining as “bb”. Only the “bb” would show as chocolate.

If the litter size was large enough—more than 100—you would probably see a distribution of colors fairly close to these percentages. However because litter size is much smaller you could get all basic blacks or all chocolates or something in between.

The yellow / not yellow gene is similar:

In this case the genes have a 25% chance of combining as “EE” (not yellow), a 50% chance of combining as “Ee” (not yellow) and a 25% chance of combining as “ee”. Only the “ee” would show as yellow.

Now let’s combine them—if both parents are black and carry the genes for chocolate and yellow they would be EeBb.

Yeowie!! The percentages break down like this:

25% EeBb (Byc)

12.5% EEBb (Bc),

12.5% EeBB (By),

12.5% Eebb (Cy),

12.5% eeBb (Yc),

6.25% EEBB (BB),

6.25% EEbb (C, no yellow),

6.25% eeBB (Y, no chocolate),

6.25% eebb (Y, chocolate nose and eye rims).

How about that chocolate bred to a yellow that produced all blacks? Was that a mistake?

Well, let’s see. Dad is EEbb (chocolate) and mom is eeBB (yellow). All of their offspring will be EeBb which means the dominant form of “E” is not yellow and the dominant form of “B” is black. So, all of the puppies will be black, but will carry the genes for chocolate and for yellow.

You can also work backwards from the children to the parents. For example, if a black male has even one chocolate puppy in his lifetime, he is Bb. If he’s been bred to a few yellows and never produced a yellow puppy, he is probably EE. We wouldn’t know for sure, but if he’s had 20+ puppies out of yellow mothers and none of the puppies are yellow, he probably doesn’t carry yellow.

If a yellow female has been bred to a black male and they had black and yellow puppies, but no chocolates, what would you conclude? Well, we know dad carries yellow, but doesn’t show it so he’s Ee and mom is yellow so she’s ee. Because dad is black he must have at least one B, but we don’t know anything about the other in the pair. He might carry chocolate while the mother doesn’t have it or she might carry chocolate and he doesn’t or it could be that neither carry chocolate or they could both carry chocolate and Mother Nature just didn’t pair the genes for the chocolate to appear. So dad would be EeB? and mom is eeB? (where the ? means an unknown gene) unless she has a chocolate nose in which case she would be eebb.

By the way, that polar bear white we talked about - it's really a yellow with very light pigment. The silver? It's not a correct Lab color and would be disqualified in the show ring. Some people feel it's a chocolate with very light pigment - like the polar bear white. Other people feel a chocolate Lab had been crossed with a Weimaraner - deliberately or not - to produce the diluted color. With all the genetic tests coming out, it's only a matter of time before we know for sure.

Powered by groups.yahoo.com