By Patti Gustafson
From Pembroke Welsh Corgis in America, 1995 
(The Handbook)

I've long been intrigued with the genetics of coat color in the Pembroke Welsh Corgi and have been disappointed that so little
has been written on the subject. The only sources I have found on Pembroke coat color include a paragraph in Clarence C.Little's The Inheritance of Coat Color in Dogs (published 1957), a paragraph in Malcolm B. Willis' Genetics of the Dog (published 1989) and two articles from early Welsh Corgi League handbooks: "Colour Inheritance in Pembrokes" by Pat L.Curties in 1957 and "The Genetics of Colour Inheritance in Pembroke Corgis" by W. H. Harding in 1958. What follows is my theory on the genetics of Pembroke coat color based both on authority and observation. I have relied extensively on Little, since his is the most definitive work on coat color, but have expanded and modified his findings on the Pembroke based on my own experience and observation.

Various genes or alleles determine coat color in the Corgi. Little has identified nine separate gene bases or loci, each with a
bio-chemical part to play in the expression of Pembroke coat color. A Corgi will have a pair of alleles for each of the nine loci -
one allele of the pair will have come from the dog's sire, the other from his dam. At each locus it is possible that one allele of the
pair will be dominant over the other. A dominant or epistatic allele will have the effect of masking or prohibiting expression of
the second recessive or hypostatic allele. The outward expression in the dog's coat, then, will be that of the dominant (also
called epistatic, meaning standing above) allele. We call that outward appearance, the result we can see, the dog's phenotype.
Sometimes the dominant allele imperfect-ly or incompletely masks the recessive allele, giving the opportunity for some of the
recessive allele to be expressed. Whether totally masked or not, however, the recessive (or hypostatic, meaning standing
below) allele, will still be present in the genetic structure of the dog and can be passed to the dog's offspring where, if it is not
once again masked by the second allele of the pair provided by the other parent, it may be expressed. This genetic structure of
the dog, that we cannot see, we call the dog's genotype. Although we cannot "see" a dog's genotype, we can make educated
guesses about it from observing both the dog's parents and the dog's offspring.

This is all much easier understood in practice. Take tricolors. The locus which determines whether a Corgi will be a tricolor or
not is the A locus. At this locus the alleles that a Corgi can have are "ay," "atR" and "atb." Only the "ay" is Little's designation; I
have expanded Little's "at" gene to reflect what actually occurs in the Corgi, namely that there are both redheaded and
blackheaded tris and that the redheaded tri is definitely dominant to the blackheaded tri. The "ay" allele is dominant to the other
two ("atR" and "atb"). The presence of just one "ay' allele then will cause the dog to be "red" or "tan' rather than tricolor.
Standing below "ay" in the series is the allele "atR" which produces (when not in the presence of "ay") the redheaded tri. Though
"atR" is recessive to "ay," it is in turn dominant to the bottom most allele in the series, "atb," which is the allele for the
blackheaded tri. Tricolors, then, will have one of the following gene pairs: "atR atR," "atR atb,' or "atb atb." The "atR atR" dog
will be a redheaded tri in appearance, and genetically his offering to his offspring's A locus gene pair will always be "atR." The
"atR atb" dog also will be a redheaded tri, but genetically he will be capable of passing either the "atR" gene or the "atb" gene to
his offspring. Thus two redheaded tricolors of this genotype ("atR atb") can produce blackheaded tris among their offspring,
providing the puppy is the recipient of each parent's "atb" allele.

Let's go back to phenotype, or outward appearance of our dogs. If we have a "red and white" bitch that we are breeding to a
redheaded tri male, what coat colors can we expect in the puppies? First, it would help if we can make educated guesses about
the genotype of each parent. Does our bitch have a tricolored parent? If she did, and that parent was a blackheaded tri ("atb
atb") like Ch. Windyle Extravagance, then we know that our bitch's genotype must be "ay atb." Why? Because she's "red";
therefore one allele of the pair must be "ay." Tux, being a blackheaded tri, and having only "atb" or "atb" to pass on, cannot have
given the bitch the "ay" allele. That must have come to her from her dam. However, Tux has contributed the second allele of the
pair and that has to be "atb" - it's all he has. Thus our bitch is "ay atb."

On the other hand, if our bitch's tri parent was a redheaded tri, say, Ch. Nebriowa Jovan, then we know that she will carry
either "atR" or possibly "atb," but we can't be sure which. Why possibly "atb," when Joey is a redheaded tri? Because "atR" can
mask the "atb" allele. In fact, a little more study will show us that Joey must be "atR atb" since his dam was the blackheaded tri
Woodhenge Black Velvet. Since Joey is a redheaded tri, he must have one "atR" allele. That would have come to him from his
sire, Ch. Nebriowa Christian Dior. From his dam he can have inherited only "atb." Thus Joey is "atR atb," with the redheaded
gene masking the blackheaded gene. And his daughter, our "red and white" bitch, can now be designated "ay at?" (i.e. she
carries the tri factor, but we don't know which kind).

So let's say that our "red and white" bitch is a Tux daughter and is "ay atb." If she's mated to a redheaded tri like Joey, whom
we know is "atR atb" in genotype. We could get puppies that are "reds," redheaded tris and blackheaded tris. But just because
these three colors are possible, does not mean we will get all three. Each puppy created is like a roll of the dice. It could come
up "ay atR" and thus a "red." It could be "atR atb" and thus a redheaded tri. It could be "ay atb" and again a "red" or it could
come up "atb atb" and the puppy is a blackheaded tri. In four rolls of the dice you could have one of each type, or two of two
different types, even, conceivably four of the same type. But knowing both the bitch's and the dog's genotypes, we won't be
surprised when we get a blackheaded tri. Even if the extent of our knowledge of both bitch and dog's genotypes is "ay at?" and
"atR at?," we would know that it is still possible that either or both carry the blackheaded tri gene. If any blackheaded tri
puppies are produced then it is a certainty that both carry the "atb" allele and we can remove the question marks. But the
reverse is NOT true. Just because no blackheaded tris were produced in this litter does NOT mean that neither parent carries
the "atb" allele.

If the "red and white" bitch that we are breeding did not have a tricolor parent, then we have less information to work with. The
bitch's "red" parents could have been "ay ay' (pure for red), "ay atR" or "ay atb." And depending which of each parent's gene
pair was given to the daughter, our bitch could also be any of those three genotypes. Again, observation perhaps can aid us. If,
for example, any of the bitch's littermates was a blackheaded tri, then we know her parents each had to be of the "ayatb"
genotype. Our bitch, therefore, will be either "ay atb" or "ay ay." If we breed her to Joey and get no tricolors, we will suspect
that she is the latter.

So far, concerning the alleles at the A locus we know that tricolors will be "atR atR," "atR atb" - both of which will be
redheaded tris, or "atb atb' - a blackheaded tri. We know that "reds" will be "ay ay," "ay atR" or "ay atb. " But what of sables?

Little, in his discussion of Pembroke color, makes no distinction between "reds' and sables. He would have them genotypically
the same. However, he does state in his discussion of the alleles of the A locus that "Most sable-tan dogs showing various areas
of persistent dark pigment are probably "ay at" [or for our purposes "atR" or "atb"] in genetic construction."

It is my hypothesis that sabling comes from an incomplete or imperfect "ay' allele, which I call ay minus ("ay-"), and which in the
presence of the tricolor allele, especially the blackheaded allele "atb," allows some black pigment to be expressed in areas of the
coat. I tend to think of the "ay-" allele much as the "y" gender gene - which would have been an "x," only part of the leg of the
"x" is missing. Thus, when the "y" is paired with an "x," whatever is coded on the leg of the "x" that the "y" doesn't cover is
expressed. This, of course, is how we get sex-linked disorders such as hemophilia. In the same way, the "ay-" or incomplete
"ay" allele when paired with the tricolor gene allows the unmasked or unpaired portion of the tricolor gene to be expressed, and,
like the "y" gene for the male gender, I think the "ay-" allele is passed on as an "ay-." The existence of an "ay-" allele allows for
the distinction between the red and white dog carrying the "atb" allele and the sable and white dog carrying the "atb" allele. It has
been my observation that the latter ("ay- atb"), when bred to a blackheaded tri, would produce no "red" offspring, only sables
and blackheaded tris, and that the former ("ay atb"), bred to the same blackheaded tri, would not produce a sable, only "reds"
and blackheaded tris.

Remember, though, that a dog could be "ay ay-" in genotype and would be a "red" in appearance, but if bred to a blackheaded
tri, could produce both sables and reds, depending on whether the particular puppy got the "ay" or the "ay-" allele. This may
have been the source of the old formula for getting sables: "breed a pure for red dog to a blackheaded tri." Certainly it would
have been noteworthy when, on breeding a red and a blackheaded tri, you got sables. I would expect that Ch. Virginia of Fox
Covert, who was a pale red but whose sire was a sable, was probably of this "ay ay" genotype. Certainly it's true that when
bred to the blackheaded tri, Ch. Nebriowa Duskie Lad, she produced the dark sable, Ch. Martindale Peter Herring, who
would have inherited the "atb" allele from his sire and, under my theory, the "ay-" allele from his dam. I would expect that most
sables, especially the full, darkly marked sables, are "ay- atb" in genotype. The partial sables (sabling on the head but not on the
back, or sabling on the back but not on the head) may well be "ay- atR" or even in some cases "ay- ay-." It has also been my
experience that if you start with a dark sable bitch, the children and grandchildren of that bitch will be lighter sables than their
dam, unless the dam's "ay-" allele links up with another "atb" allele in the subsequent puppy. Thus the dramatic, full, dark sable
coat color seems dependent on the "atb" blackheaded tri allele. 

So now to review, I would say that the following A locus genotypes are possible in the Corgi: 

     "ay ay" - a "red" dog. "ay ay" - a "red" dog carrying the hypothetical sable "allele." "ay atR" - a "red" dog carrying the
     redheaded tri allele. "ay atb" - a "red" dog carrying the blackheaded tri allele. "ay- a)-" - a very light sable or even
     possibly a "red." "ay- atR"- a lightly marked sable. "ay- atb" - a dark sable. "atR atR" - a redheaded tri. "atR atb" - a
     redheaded tri who carries the blackheaded tri allele. " atb atb" - a blackheaded tri.

Also, "ay ay," "ay ay-," "ay- ay-" would all be "pure for red or sable," as none of these genotypes will produce a tricolor.

You perhaps will have noticed that I have used the terms "red" and "reds" - in quotation marks. That is because these terms
generally encompass colors ranging from dark reddish tans to clear reds to golds and fawns. At this point, when I speak of red,
without the quotation marks, I will be referring to those dogs with the red pigment in their coat, differentiating them from those
whose "red" is actually tan, or gold or a sandy-beige fawn.

The red dog of yesterday is rapidly disappearing. Those that were called variously, "deep red," "dark red," "rich fox red," "bright
red" are hardly to be seen anymore. The last PWCCA Best of Breed that I remember being described in such terms is 1983's
Ch. Garvin's Summer Color CDX, whom Pat Curties described as, "A very striking bright, rich red bitch." And judging from
comments made in critiques through the years by British judges, the truly red dog was a rarity in the UK long before he was
here. Why is the red dog, when we can find one, a light red or golden red? Why are the majority of our dogs now goldens and
fawns? Will another ten years find us with just fawns and creams?

There are two theories on the phenomenon of color paling. The first concerns Little's C locus. At the C locus, the topmost allele
"C" allows full depth of pigmentation. Standing below "C" is "cch" the chinchilla allele, which causes a reduction in both the
number and the size of the pigmentation granules. The red and yellow pigments are affected before and more extensively than
are the black and brown pigments. In breeds having the "cch" allele, the coat colors of red and yellow animals may show
gradings of colors, with "C C" animals having the darkest coats, "C cch" animals an intermediate color and "cch cch" animals
having the palest coats. Little felt, however, that Pembrokes carried only the "C" allele.

If, on the other hand, the "cch" allele is found in the Pembroke, correcting the paling would be a relatively simple matter of just
breeding to "C C" animals, whose dark red or tan coats would be readily observable. Given the preponderance of pale coats in
today's Pembrokes, one would have to conclude then that either we have purposely been selecting against red coats or that
breeding to red or darker coated animals hasn't slowed down our slide towards beige. If we have been selecting towards paler
coats, then "C C" individuals may now be scarce in our gene pool and the majority of individuals would be "C cch" or "cch cch.
" By breeding "C cch" animals together it is still possible to get some "C C" animals. At the point, however, where all or nearly
all corgis are "cch cch," the red coat is forever lost.

If we have not been selecting against the red Corgi coat, on the other hand, a second theory concerning paling may explain why
we have still had difficulty getting and keeping the red and darker tan coat colors. A Russian, N. A. Iljin, writing in 1932 and
1934 held that a further series affects the intensity of tan coloration in the dog. The series consists of three genes: the dominant
"Int" dilutes tan towards a dirty white; the next step down in the series "intm" dilutes tan towards a light yellow or fawn; and the
lowest of the series "int" results in no dilution. Here the alleles for the truly red or tan coat would be recessive. Thus if you bred a
paler coated animal to an undiluted colored animal, you would still get coat colors that were diluted, but would carry the allele
for undiluted pigment. It would only be by breeding that generation to an undiluted colored animal that you would see some
undiluted or truly red or tan coats. It has been suggested that incomplete dominance plays a large part in Iljin's "Int" series so
that the six possible genotypes can give six shades of dilution ranging from "Int Int" with the most dilution to "int int" with no
dilutions. Such a theory would better explain the many varying shades of red, yellow and tan in the Corgi and would also help
explain why the now established pale colors are in the majority and seem so hard to get rid of.

If we were to designate the palest fawns and sands "Int intm"; the light reds, golds and fawns "Int int" or "intm intm"; the bright
reds and rich golden reds as "intm int" and the deep reds, dark tans and dark sable reds "int int" we would pretty much cover
the varying shades of Corgi coat color and would need to be prepared to see the occasional cream coat of the "Int Int"
individual, of which there is now an occasional one occurring.

The age old remedy for correcting paling, which either we're not using or it doesn't work, is to keep breeding back to a tricolor
every so often. Pat Curties mentions this in her 1957 article in the Corgi League handbook, "Colour Inheritance in Pembrokes,"
saying, "Although some people do not agree, I think that to obtain a good red, it is important to keep an infusion of pure
tricolour or pure black and tan running through a strain, otherwise the colour in succeeding generations tends to become lighter
and lighter, until eventually the majority of the puppies become a light, rather unattractive sand colour with a lot of cream shading
around the face."

W. H. Harding expresses the same thought in his 1958 Corgi League article, "The Genetics of Colour Inheritance in Pembroke
Corgis." "It is a peculiar fact, that the black gene appears to have a stimulating effect on the red. A strain which is entirely free
from the black gene tends to degenerate to a pale fawn or golden colour..." It is interesting that both Miss Curties and Mr.
Harding associated the bright and dark reds with the "atR and atb" genes themselves and not with the darker reds or tans that
are often part of, or at least used to be, the black and tan or tricolor coat. Miss Curties goes to some length to differentiate
"pure tricolour" from "black sables" which are sometimes (or were) also designated as tricolors or black and tans. So when she
says "pure tricolour" she is referring to the "atR" and "atb" genes. Mr. Harding, too, finds that it is the tricolor gene itself, not the
darkness of the red or tan accompanying the black that has the influence on the red coat color. "If a bitch of this strain [which is
entirely free from the black gene] is mated to a tri-colour dog, the puppies are likely to be a much brighter red and white, but
there will be no tricolours [thus the bitch is "ay ay" or "ay ay-"]. However there may be some sable puppies."

Derek Rayne, however, in an October 1985 interview given to Corgi Quarterly, states, "We don't want to get Corgis too light a
brown; if you keep breeding two light reds together, eventually you will get a dog who is almost a beige color which is not good.
I used to try to use a dark red or tricolor in my breeding every once in a while to strengthen the red tones back into more of a
fox red which is the original color and which you don't see too often anymore. We do have some of these sandy shades now
which look rather washed out."

The reds and tans of tricolors and sables are just as influenced by the "cch" allele or the alleles of the "Int" series, as are the "red"
dogs. Base coats for sables are also lighter now, in many cases, as are the accompanying red or tan in the tricolor. Many
tricolors, black-headed tris included, are now black, fawn and white rather than black, tan and white or black, red and white.
So, old remedy aside, it appears that the "black gene," of and by itself, really has no influence on the red or tan pigmentation.
Instead, it would appear that what had been working for breeders was the selection for the dark red and tan, which in the past,
often went hand in glove with the tri-color coat color.

Having disposed of the basic coat color types in the Pembroke, we come now to the white spotting factor. Little's S locus is the
location for alleles dealing with white on the Corgi. The topmost allele at this locus in "S" giving the solid colored dog. A good
portion of the earliest corgis carried the "S" allele, and were solid red without white. Standing under the "S" allele is the "si" allele
for the "irish spotting" pattern. This pattern places white spots or streaks in one or more of the following locations: muzzle,
forehead star or blaze, chest, belly, one or more feet, tail tip.

These are the two alleles (of the four possible at the S locus) that Little finds in the Pembroke. However the alleles of the S
locus are greatly influenced by modifiers. These modifiers called "plus" if they influence towards more pigment and less white
and "minus" if they shade towards more white and less pigment, can have the effect of moving the "si" allele, for example,
towards the phenotype of the "S" allele when accompanied by lots of plus modifiers or towards the phenotype of the next allele
in the series, the "sp" or piebald allele (which allows for white spots or streaks almost anywhere on the body), when
accompanied by lots of minus modifiers. Thus two very flashy dogs, with lots of white, when bred together, may produce one or
more puppies who have white in places not associated with the "si" allele, such as on their backs or on their ears. We would call
these mismarks.

To avoid mismarks, it would seem judicious to breed a very flashy dog, one with maximum white, to a plainer, less flashy dog,
thus balancing minus modifiers with plus modifiers. Interestingly, many Corgi breeders feel that the modifiers play a more
regional role. For example, a dog with a large muzzle spot and a wide white blaze, but very little while on the neck or the stifle,
can successfully be bred to the plainer faced dog who sports a full white collar and a fair amount of white edging to the stifle.
Thus the minus modifiers for head white would be balanced with the other dog's plus modifiers, and the plus modifiers for body
white would balance the other dog's minus modifiers.

Where you are more apt to get mismarks is by doubling up the minus modifiers for head white, often leading to white on the
ears or over too much of the face, or by doubling up on minus modifiers for the body leading to white over too much of the stifle
or creeping up from the belly too far onto the flanks.

Of the nine loci that Little has identified as playing a role in the Corgi, we have discussed three (A, C and S) and one series
(Iljin's "Int" series) that Little does not identify. To conclude this article, let me quickly identify the other six loci and the alleles
that Little finds applicable to the Corgi at each.

The B locus, which determines whether the dark pigment will be black ("B") or liver ("b"). Little finds only the "B" allele in the
Corgi.

The D locus which determines the intensity of pigmentation. The dominant "D" allele causing intense pigmentation and the
recessive "d" allele diluting the pigmentation towards a dull, silvery shade. The overwhelming number of Corgis are "D D," but
those individuals who are "D d" when mated together can produce the "bluie" coat color ("d d"). 

The E locus determines the extension of dark pigment in the coat. The "E" allele acts to extend dark pigment evenly over the
body and thus is in conflict with the "ay" allele of the A locus, which is acting to restrict the dark pigment. Standing below "E" is
"ebr" which gives the brindle coat color in the Cardigan and in a few early Pems. The last of the series is the "e" allele, which
acts to restrict dark pigment entirely. In many breeds the red coat color is derived from the solid black allele of the A locus "A"
in conjunction with the recessive, restrictive "e" allele from the E locus. In many of these breeds there is only one allele from the
A locus in the gene pool, "A" and whether the dog will be black or "red" is strictly determined by the presence of "E" (a black
dog) or of "ee" (a "red" dog). Little finds only the "E" at work in the Pembroke and I tend to agree. There are those who argue
that the "e" is also in the gene pool, but if that were so then I would expect hear of a fair number of "red" dogs ("atRatRee" or
"atbatbee") who when bred to a tricolor (e.g. "atRatREE") produced only tricolors.

The G locus concerns the phenomenon of the coat color increasingly graying and paling as the dog-matures. The dominant "G"
causes this phenomenon as in poodles and Kerry Blue terriers. Little finds only the "g," which prohibits such graying, in the
Pembroke. The M locus contains the dominant "M" which produces the merle and the recessive "m", which acts to produce
uniform pigmentation. It's the "m" that's found in the Pembroke.

The T locus contains the dominant "T" which produces ticking (ticks of color in the white areas of the coat) and the recessive "t"
which prohibits ticking. The Pembroke has only the "t" gene.

When Mary Miner asked me to write this article on coat color for the handbook, I was very flattered, but I also had some
misgivings. The challenge would be to condense into one article what had taken me three comparable articles in my series on
coat color in the Pembroke Welsh Corgi Newsletter. I wasn't sure I could streamline information and explanations and still be
"readable." I don't really feel I succeeded.

The second misgiving had to do with a comment Mary made about the handbook being a more permanent record than the
newsletter. She meant it for an enticement, but if, as I hope, much further study is devoted to the genetics of coat color, readers
ten or twenty years from now will find this article naive and simplistic and fraught with errors. On the other hand, I hope that this
article will get us all sharing information about coat color inheritance and allow us to make better, more educated assumptions
about how the various coat colors are inherited in the Pembroke. I would love to receive as much information as you would
care to share about the colors you got when your bred different individuals. I would also love to hear others' theories regarding
such not-very-straightforward topics as the sable coat color and color paling.