The E Series
The E-series determines the extension or restriction of Eumelanin (Black or Chocolate). It has no effect on Phaeomelanin (Red or Tan). However, because of the action of extension or restriction of Eumelanin, it can have a direct effect on what we see in both color and pattern.
The E-series has a co-dominance in play, with a single clear recessive:
"E" and "Ebr" are equal in dominance, while "e" is recessive to both.
E - full extension of Eumelanin color (full extension of black or chocolate in those areas containing Eumelanin).
Ebr - permits Eumelanin (black or chocolate) to form in layers through Phaeomelanin (red or tan), giving a tiger-striped appearance known as Brindle. To achieve this effect, both Eumelanin and Phaeomelanin must be present. Without Phaeomelanin ("A_"), the Brindle allele can remain visibly "hidden" or "masked."
e - restricts the formation of Eumelanin in the coat - in totality. Does not affect Eumelanin in the nose leather or eye color. Requires two recessives genes: "ee" to achieve this action of restriction.
As a dominant gene, only one "E" is required to create the action. "E" permits the full extension of available Eumelanin (black or chocolate) color. This Eumelanin can be effected by other genes, with regard to pattern (such as "ay" sable) or color such as "dd" dilution, where the color is changed from black to blue or chocolate to Isabella. "E" doesn't determine the color of the Eumelanin, only its extension.
The vast majority of Rat Terriers are "E_." A dog who is "EE" may look identical to a dog who carries "e" in the recessive "Ee," due to the dominance of "E."
At this writing, Brindle ("Ebr_") is not a recognized color pattern in Rat Terriers in the UKC, and only recognized "on the face" in UKCI. Because there are Brindle Rat Terriers, we'll discuss "Ebr" at length, below.
There are a growing number of Rat Terriers carrying a single recessive "e" ("Ee") who are capable - when bred to another "e" carrier" - of producing dogs with restricted Eumelanin. There are, therefore, also a growing number of Rat Terriers who carry the double-recessive of "ee," as seen in Apricots, Lemons and Clear Tans. We'll explore this more in a moment.
Affecting only the Eumelanin parts of the coat (black or chocolate), dominant "E" allows the full extension of the Eumelanin pigment, wherever this pigment already exists (determined by other genes). "E" doesn't create Eumelanin color - only its extension. It's important to also remember that the Eumelanin pigment can be restricted by other genes from other series. As we learned in the A-series, the gene "ay," when doubled or when carried with its recessive "at," can restrict Eumelanin into the sable pattern. But wherever Eumelanin is present, "E" allows the full extension of this pigment.
Co-Dominant Ebr (Brindle)
As a co-dominant to dominant "E," "Ebr" only requires one "Ebr" gene to produce its action.
Responsible for the Brindle pattern, "Ebr" is an often misunderstood allele. Brindle breeders will tell you, "It can't be dominant - it's so hard to reproduce!" The truth is: producing Brindle isn't difficult at all, once you understand the principles behind this gene's action: that this color pattern requires the existence of Phaeomelanin (red or tan) in order to create the tiger-striped pattern known as Brindle.
"Ebr" doesn't create Eumelanin or Phaeomelanin, but rather, it permits the extension of available Eumelanin (black or chocolate) to form in patterned layers of available Phaeomelanin (tan or red). Phaeomelanin (red or tan), therefore, has to be present in order for the action of "Ebr" to have an affect.
"Ebr permits the formation of Eumelanin pigment through Phaeomelanin areas." What does this mean?
Well, first, let's clarify what it DOESN'T mean: It doesn't mean that Ebr will suddenly "create" Phaeomelanin in areas that are Eumelanin. If an area of coat is black or chocolate, with no tan or red present, then the striped pattern will not be visible, and the "Brindle" effect will be "masked" or "hidden."
Remember, the action of "Ebr" is to allow Eumelanin to form in Phaeomelanin - not the other way around: NOT: "Phaeomelanin to form in Eumelanin." When you look at the Brindle pattern, what you're really seeing is a Phaeomelanin (red or tan) base where Eumelanin has been permitted to form in a banded pattern.
What it DOES mean is that wherever Phaeomelanin is present (tan or red), Ebr will permit the formation of Eumelanin pigment to form through these areas in a tiger-striped pattern known as "Brindle."
So, let's look at some typical colorations in Rat Terriers (A-series), beginning with a typical "atat" Rat Terrier who exhibits both Eumelanin and Phaeomelanin:
Where there is Phaeomelanin (tan or red), Ebr will permit Eumelanin (black or chocolate) to form in a tiger-striped pattern. Looking at the dog above, where on this dog will Ebr permit the formation of Eumelanin through Phaeomelanin? In the tan points. This is sometimes called "Trindle," a "tri-point dog whose tan points exhibit the brindle pattern."
If the dog above has limited Phaeomelanin in the tan-points (small tan-pointed areas), it may be difficult to recognize the Brindle pattern within this small area of the coat. The black areas on this dog will remain black (Eumelanin to form in banded patterns within Phaeomelanin, not the other way around). If the dog above had less white and more tan areas on the body (black & tan), with extension of Phaeomelanin (tan or red) on the legs, flanks, etc., these areas, too, would show the Brindle pattern.
Example of a "Trindle" Rat Terrier, where only the tan-points show the Brindle pattern:
Now, let's look at another typical pattern within the Rat Terrier; Eumelanin and White: "A_":
As we learned above, "Ebr" will permit Eumelanin (black or chocolate) to form in layers through Phaeomelanin (red or tan), but Phaeomelanin needs to be present in order for this pattern to be generated and visible. Where on the above dog will this pattern be exhibited? No where, because this dog doesn't exhibit Phaeomelanin (red or tan). Therefore, while this dog carries the genetics to produce the Brindle pattern, it does not, itself, visibly present it. The pattern requires the presence of Phaeomelanin in order to present the pattern. This dog's Brindle would be "hidden" or "masked."
An interesting note: When a dog is "Aay" (Eumelanin and White, but carrying a single "ay" or sable gene in the recessive) it's sometimes possible to see a faint Brindle pattern within the black coat in direct or bright sunlight.
Now let's look at another common color pattern in the Rat Terrier: "ayay," or "ayat" (Sable):
Again, the "Ebr" gene will permit the formation of Eumelanin (black or chocolate) to form in layers through Phaeomelanin (red or tan) in a tiger-striped pattern known as "Brindle." If the sable dog above carries "Ebr" (Brindle), either as "EEbr" or "EbrEbr," then where in its coat will this pattern emerge? Everywhere there is Phaeomelanin pigment. Since a sable dog is "Phaeomelanin Dominant" (dominant red or tan base), all pigmented areas on this particular dog will exhibit the Brindle pattern.
Example of a full Brindle pattern on a Rat Terrier:
So if want to breed for a VISIBLE Brindle pattern, it is necessary to introduce the "Ebr" gene to dogs who carry Phaeomelanin (red or tan). The more Phaeomelanin pigment on the dog, the more Brindle pattern that we'll see, or which will exhibit visibly.
Since "Ebr" is dominant (alone, or as a co-dominant with "E"), it only requires one carrier of "Ebr" in the pair in order to reproduce the Brindle trait. But in order to visibly see the trait, Phaeomelanin (red or tan) must be present.
Therefore, the difficulty in producing visibly Brindle dogs doesn't lie in whether or not the gene is "dominant" (it is dominant, requiring only one in the pair to carry it in order to reproduce the trait in their offspring), but rather that its visibility relies dogs who exhibit Phaeomelanin from which the Eumelanin may create its banded pattern. Brindle's ability to be "masked" or visibly "hidden" in coats that do not exhibit Phaeomelanin, but exhibit Eumelanin only - black, chocolate, etc. - is why some breeders have felt that Brindle is more difficult to control, once introduced into a line.
As a dominant gene requiring only one "Ebr" allele in the mix to reproduce the trait, it's reasonable to recognize that the more "Ebr" going in, the more Brindle that will produced. For example, imagine a pair of dogs where one is "EE" and the other is "EEbr." In this scenario, we have only one "Ebr" gene that will be introduced. Each dog gives ONE of each of its pair to its offspring: E E x E Ebr. All the offspring, therefore, will receive an "E" gene from the "EE" carrying dog. Some of the offspring will receive "E" from the "EEbr" carrying dog, and some will receive "Ebr."
E E x E Ebr (producing one pup with Brindle):
Pup #1 = E E | Pup #2 = E Ebr | Pup #3 = E E | Pup #4 = E E | Pup #5 = E E
Pup #1 = E E (not brindle)
Pup #2 = E Ebr (Brindle)
Pup #3 = E E (not brindle)
Pup #4 = E E (not brindle)
Pup #5 = E E (not brindle)
Now let's introduce two dogs carrying Brindle. We now have more Brindle going in to the mix, with a larger potential outcome of Brindle Offspring:
E Ebr x E Ebr (producing three pups with Brindle):
Pup #1 = E E | Pup #2 = E Ebr | Pup #3 = Ebr E | Pup #4 = Ebr Ebr | Pup #5 = E E
Pup #1 = E E (not brindle)
Pup #2 = E Ebr (Brindle)
Pup #3 = Ebr E (Brindle)
Pup #4 = Ebr Ebr (Brindle)
Pup #5 = E E (not brindle)
An even greater number of Brindle will be produced when one of the pair carries the Brindle gene, doubled: "Ebr Ebr," meaning that every pup in the litter will receive the "Ebr" gene - however, only those pups who also exhibit Phaeomelanin (tan or red) will exhibit the trait, visibly:
E E x Ebr Ebr (producing five pups with Brindle):
Pup #1 = E Ebr | Pup #2 = E Ebr | Pup #3 = E Ebr | Pup #4 = E Ebr | Pup #5 = E Ebr
Pup #1 = E Ebr (Brindle)
Pup #2 = E Ebr (Brindle)
Pup #3 = E Ebr (Brindle)
Pup #4 = E Ebr (Brindle)
Pup #5 = E Ebr (Brindle)
So, even breeding in a Brindle to Brindle breeding you may produce less Brindle offspring than breeding a non-brindle to a Brindle carrying "Ebr" doubled: "Ebr Ebr."
As a recessive gene, two "e" alleles are required ("ee") in order to create this gene's action: to restrict Eumelanin (black or chocolate) in totality from the coat, but not in the nose leather or eye color.
We can see this gene in action by looking at the two pups below, who are littermates. Major, on the left, carries "E_", his sister, on the right, "ee":
Genetically, these two dogs are the same, except for "ee." The double-recessive of "ee" in Rose's color genetic string has restricted her Black Eumelanin from forming in her coat. Without "ee," Rose would be a Black & Tan, just like her brother. With "ee" and the total restriction of Eumelanin from her coat, Miss Rose is a rare Clear Tan.
If you look very closely at Rose's picture, you may notice that the tan areas of coat where black would have formed, if it had not been restricted by "ee," is a slightly different color than the tan in the points on her legs and muzzle. You can almost make out where the black would have been, if it hadn't been restricted by "ee." This is because Rose is "atat" in the Agouti string. If she had been genetically sable, with "ee" restriction, her tan coat would have been more uniform in color. This distinction is most apparent in puppyhood.
These two are so cute, I think they deserve another look:
We now know that "ee" affects only Eumelanin, and we learned in the lesson on the C-series that the gene "cch" primarily affects Phaeomelanin - so an interesting thing happens when these two genes come together, in their respective double-recessives: "ee" x "cch cch."
First "ee" restricts the formation of Eumelanin (black or chocolate) in the coat, and then "cch cch" comes along and dilutes any remaining or existing Phaeomelanin (red or tan). In some cases, this dilution is to nearly white. The coloration then develops further as the dog matures.
Depending on the other genes in play (B, b, D, or d), this produces colors commonly known as "Lemon" or "Apricot":
And here's another of beautiful Kirby, all grown up:
To see more pictures of beautiful Lemons and Apricots, see Lesson #4.
There's another gene in this series that I've purposely omitted. "Em" produces a Eumelanin mask on the muzzle, usually seen in predominantly Phaeomelanin dogs, and is considered a disqualifying color in Rat Terriers.
It's worth mentioning, however, because the word "mask" can be confusing. When they say mask, they don't mean our tan-point mask that looks like this:
And they also don't mean the Calico "mask" of Phaeomelanin (red or tan) on the face.
What they mean is more of the bandana-cowboy-type of Eumelanin (black or chocolate) mask that covers the lower portion of the face, while the rest of the face is Phaeomelanin - that kind of mask. Follow that? I have seen a few Rat Terriers exhibiting "Em," but I'm not posting their pictures here - mostly because I don't understand why it's a disqualifier, and also because these dogs have apparently been registered with UKC without an issue. If you look up this allele on other breeds, you'll get a clearer picture regarding what "mask" really means in this regard - including illustrations of "Em" dogs in other breeds.
Copyrightę2006 Sue Campbell - All Rights Reserved