Locus - The location of a series of genes. Each gene series is
referred to as a ‘locus’.
Gene Series - A set of genes that controls a related set of
Dominant - A "strong" gene which masks, or trumps, the
presence of other genes at its own locus. A dominant gene
needs only one copy for it’s trait to be expressed. If paired
with a recessive gene, the dog is said to be ‘carrying’ the
recessive gene. ‘B’ is the designation for the dominant
black gene, ‘b’ is for the recessive chocolate gene. A Bb dog
is black carrying chocolate. Note that in this article, if only
one gene, a dominant one, is shown, the other gene is
assumed but not indicated, as it’s presence does not affect
the phenotype. For example, if a genotype is listed as Bdd,
there IS another B series gene present, either a ‘B’ or a ‘b’,
but it is not written. Another way of designating this would
be to write it Bxbb.
Recessive - A "weaker", or hidden, gene which must be
present in double combination in order for it's effects to be
shown. So if ‘b’ is recessive chocolate, a dog must be ‘bb’ to
have chocolate coloring.
Carrying - The presence of a recessive gene paired with a
dominant gene. In this case the recessive gene can be
passed to progeny, but its effects cannot be seen in the dog
carrying it. So Bb is Black (B) carrying chocolate(b).
Phenotype - The visible appearance of a gene's effects -
example: "Bb" - phenotype is black. PHenotype is the
PHysical appearance of the dog.
Genotype - The genes carried, but not necessarily with
visible effects - example: "Bb" - genotype is black(B),
carrying chocolate(b). GEnotype is the GEnetic make-up of
The E Series
Dogs have two major types of pigment granules in their coats. The production
of the pigment granules is controlled by something called the Extension genes or
the Extension series. One type of pigment is red/yellow (pheomelanin), the other
is black/brown (Eumelanin). The black/brown type of pigment is dominant to the
yellow kind of pigment, so the designation for the black/brown pigment is E (for
Eumelanin). The gene for the recessive, yellow/red pigment, is e. If an E is
present, dark pigment granules will be produced, but if the genotype is ee,
yellow/red pigment granules will be produced. An E does not tell you if the dark
pigment will be black or brown, however. Another gene series (B Series),
discussed below, controls the SHAPE of the pigment granules, and, depending on
the shape, the granules will look black or brown. It’s important to realize that the
E series genes contribute to COAT color, not eye, skin or nose pigmentation. A
dog has to have at least one E in order to have any brown in the coat. ee is
yellow/ red because the darker, Eumelanin pigment, is completely prevented from
forming. One important thing to remember for later is that the dominant E allows
expression of genes of another series, the A series. The recessive ee overrides
the A series and completely masks it. More on that later!
Another variant of the E gene is Em,a melanistic mask where the muzzle is black.
This is often seen in Afghans and Great Danes, sometimes in poodles and there
for in Doodles. Em is dominant to E.
The B Series
The B gene, or B series, affects, coat, nose, skin and eye color. It affects the color
by changing the shape of the pigment granules produced by the Extension
gene. The B version, which is dominant, will cause black pigmentation in the
nose and cause the Eumelanin in the coat, made by the extension, gene to look
black. The b version, which is recessive, causes the nose pigment to appear
brown, and causes the Eumelanin in the coat, made by the Extension gene, to
look brown. As with all dominant genes, only one has to be present for it to be
expressed. That is, BB and Bb will show as black, bb will be brown.
E and B Series Interactions
Let’s stop here and see how the E gene and the B gene can interact. If the dog is
ee, there IS no dark Eumelanin, the only pigment the coat produces is the
yellow/red Pheomelanin pigment, therefore the dog’s coat will be in the yellow/red
spectrum. If the dog then has 2 recessive B series genes, bb, the shape of the
pigment granules causes the dog to have a rose, liver or brown nose. So an
bbee dog would be yellow/apricot/red coat with a rose/liver/brown nose. If the
B gene is present, the nose will be black. It doesn’t matter if it is Bb or BB, the
nose will usually be black. An BBee, or an Bbee dog is yellow/red with a black
nose, although occasionally a Bbee dog will have a nose that is lighter. If that dog
has an E gene, the dark, instead of yellow pigment will be produced in the coat.
So BbEe, BBEE, BBEe, and BbEE would all be black dogs with black noses.
However, if the dog is bb, the granule SHAPE will make it appear brown instead of
black. So an bbEe or bbEE dog has a chocolate coat with a brown nose.
Beyond E and B
The genetics discussed up to this point is the genetics familiar to most, as it
explains in its entirety the genetics of coat color in Labradors, and all these genes
can be determined in readily available lab tests. In other words, people can send
in a cheek swab and find out if their dogs carry these genes. However, once
poodles enter the picture, the coat genetics complicate considerably, and not all
the genes can be tested for by commonly available means.
The A Series
There is a gene series called A, for Agouti, that controls where in the hair shaft
pigment is produced. The 3 versions of this are Ay, which can cause a red color
with black hair tips, commonly called a sable at, which causes phantoms, and a,
If a dog is ee however, the A series is short-circuited, and it will not be expressed
at all! In addition, it appears as though very interesting things happen in crosses
between Poodles and Goldens due to genes at the A locus. Every Golden has
genes at the A locus, but their expression in masked by the ee genotype which
doesn't allow any dark pigment to be produced. So for Goldens, the content of
that entire A series is an unknown, only to be revealed when crossed and
unmasked! Breeding a Golden to a Poodle with the at phantom gene often
results in phantom Goldendoodles, meaning that Golden had a masked at gene.
Sometimes a litter with unexpected black puppies can result from a Poodle with
one a gene and a Golden with a masked a gene.
The K Series
Another gene series important in poodles is the K series (coming from the word
blacK). The K is a dominant dark color over the whole coat, and overrides
almost all other genes. Notice that I said K causes dark colors. Whether that dark
color is black or chocolate depends on the B series. A dominant B gene will
produce black in a K dog, but the same K will produce brown in a bb dog. A
second variation in the K series is k, causing a recessive, non- dark coloration.
When a dog is kk, it is like a clear window, it allows other colors and patterns,
those in the A series, to show through. K is like opaque glass, nothing shows but
dark, covering up the A series. A final variation in the K series is kbr, a recessive
gene causing brindle coloration. K is dominant to kbr, which in turn is dominant
to k. The important thing to realize about this series is that dominant K trumps
AMOST everything at every other locus. The dog WILL be dark at birth with this
gene, with two exceptions. The first was mentioned earlier, if the dog is ee, and
the only pigment it CAN produce is yellow/red, then it will be yellow/red!
The S Series
This Series is responsible for the pattern of color called Parti, and is caused by a
variation called sp. This gene is recessive to the dominant allele, S, which causes
solid coloration. The sp/sp genotype causes patches of dark color on a white
background. Which dark color is expressed depends on the other genes
present. An ExBxspsp dog would have patches of black, while an Exbbspsp
dog would have patches of chocolate.
The Dilution Gene
The one other thing that can alter the expression of the K gene is the presence of
a recessive dilution gene. The dominant D gives full color, the recessive version is
d, and causes colors to become diluted if 2 copies are present. So a Kdd dog,
black at birth, will ‘dilute’ to blue, a chocolate,bbdd, will dilute to beige or cafe.
Putting It Together
So the E, B, K and A loci act together like this:
If the B-locus is B, the coat and nose will be black UNLESS the dog is ee.
If the B-locus is bb, the nose and coat will be brown UNLESS the dog is ee.
If the E-locus is ee, the coat is yellow/red; This makes things easy. It does not
matter what other genes are present! What is not so easy is figuring out what
genes there are at the K locus and A locus, because you can’t see any evidence
If the E-locus is EE or Ee and at the K-locus is a K allele present, the coat is
If the E-locus is EE or Ee and at the K-locus either kbrkbr or kbrk is present the
coat is brindle;
If the E-locus is EE or Ee and the K-locus is kk, the A-locus determines the coat
color (Ay or at or a). So all dogs with tan points (at) are kk. Similarly, all dogs
whose red color is caused by AyAy are also kk. These AyAy dogs do not have
the black tips because their ee genotype prevents the production of that dark
So the question arises for red dogs, are they ee or AyAy? Sometimes that is
difficult to assess. But some researchers (see Sue Ann Bowling's article) suspect
that ee dogs are a ‘clear’ red, with no black anywhere, and that AyAy red dogs
often have black whiskers, and are born with coats that are dark and lighten.
Those red poodles that fade to apricot are probably AyAy, unless they are eedd!
(That is, red, but diluted).The AyAy genotype can be a fooler, if one has
assumed that all apricot dogs are 'ee'. One would expect two apricot dogs to
have only apricot pups. But if one of those dogs is apricot due to AyAy then
black and chocolate pups can occur in the litter. That is what happened here:
Delight, the parti poodle seen below, could easily be mistaken for an apricot and
white (Bxee) poodle. If that were true and he was bred to an F1 Labradoodle
(Bbee) all puppies would be expected to be cream. But this is the litter that
Delight (AyAyBbEe) is a sable, not an apricot, and his genotype ofAyAyBbEe
produced black and chocolate pups when bred to a Bbee F1 Labradoodle.
It can be pretty overwhelming to look at a string of letters in a genotype and
decide which to think about first. It’s even harder to LOOK at a dog and decide
what it's possible genotypes might be! So let’s try prioritizing the gene series. The
first thing I would look at is the E series. If it is ee the dog is yellow/red.
Conversely, a yellow/red dog is most likely ee (although you should review the
part on the ay series, as that is possible!). But if there is an E in the genotype,
the dog is geneticallysome color other than yellow/red, even if the appearance is
Next I would look at the B series. If it is bb the dog will be in the chocolate
spectrum, unless you already determined it was yellow/red (ee) in which case
only its nose will be brown. So if the dog has an E and a B, you know it is making
black pigment in both it’s coat and nose areas, but if it is E and bb, that pigment
is chocolate instead.
Next in line would be to look at the K series.....where in the coat the color
appears. The K would mean it is solid dark all over. kbrkbr or kbrk would mean
the color is in stripes (brindle). kk is that clear window looking at the A locus.....
meaning the color is determined by the A locus. This is where Ay (red) would be
evident, or at (phantom or black and tan points), or a, recessive black. All dogs
displaying at, Ay or a genes phenotypically are also k/k. Notice that a dog could
carry either the a, Ay or at, but if it was a K, those traits are impossible to see, as
they are covered up by the solid dark K gene.
Regarding the Golden Retriever Genotype
Golden Retrievers are commonly assumed to be genotype eeBB. I spent quite a
bit of time trying to track down an Goldens with brown or liver noses (meaning
they were eebb) and found only one instance. My feeling is that if there were
very many Bb Goldens out there, we would see Goldens with liver noses more
often. So I have concluded that the vast majority are BB. Because they are ee,
the genotype at the A series is masked, but pf course present. The possible
variants are the same as for all others, at,Ay and a, but it is impossible to know
which of these are present until the dog is crossed and they are expressed.
Thanks to Sue Ann Bowling and Sheila M. Schmutz for their great articles on dog
color genetics, I learned whatever I understand of dog color genetics from them!
Author: Helene Roussi
|eeBb, on left, next to eebb
|Sable pup with Em,
|Kona is bbEe
|Chocolate (bbEe) Phantom
|Bear is kbr/k, a brindle F1B
|Bono is an BbEe
|Brindle kbr/k F1B puppy
|Cider is Bbee
|Photo courtesy of Kathy
|Cooper is bbee