Labradoodle/Goldendoodle/North American Retriever Color Genetics

DEFINITIONS

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 traits.

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 dog.


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, recessive black.

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 of them!

If the E-locus is
EE or Ee and at the K-locus is a K allele present, the coat is dark;        


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 pigment.

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 resulted:

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 yellow/red.

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
 

 

The dilution gene at work. The pictures above are both of Keegan; 6 months of age on the left, one year of age on the right