The C Series
The genes or alleles in the C-series permit the expression or restriction of melanin. This doesn't mean that the "C" gene determines the depth or richness of color (although you might think so, on visual inspection), but rather that the "C" gene permits (or restricts - sometimes completely) the expression of the pigment producing chemicals known as melanin.
At the top of this series is dominant "C" - where melanin is expressed completely. At the other end of the spectrum is "cc," or albinism, where the total expression of melanin has been prohibited, producing an animal with no melanin in its skin, coat (hair) or eyes - Albinism.
Most Rat Terriers are "C_," permitting full expression of the melanin they carry. Fortunately, I have not been able to find a single example of a "cc" (or albino) Rat Terrier.
In the middle of this series is an interesting little gene known as "cch." As we read further, we'll learn that "cch" has a greater effect on Phaeomelanin than on Eumelanin, and when the double-recessive of "cch cch" is combined with the double-recessive "ee," it can produce a color that has an interesting development as the dog matures, under the colors currently listed as "Lemon" and "Apricot," but actually containing a wider range of color genetics than these two names would imply.
Genes in the C-series don't determine the amount of color or the placement of color, but rather permit the available color (melanin) to click on and express. Think of "C" like a light switch. Turned on, "C" or, in a more limited way "cch," allows the chemicals of melanin to express pigment. Turned off, "cc," (despite the fact that all the other chemical components may be in place to produce color - "A" and "B" series), pigment is unable to express. The switch is "off," and what results is the total absence of pigment (albinism).
The vast majority of dogs are dominant C, Rat Terriers included. As a dominant gene, only one "C" allele is necessary to allow full expression of pigment, or melanin. While "C" doesn't determine the richness or depth of color (other genes in the other series determine that), "C" is necessary to allow full expression of pigment. It's pigment with the light switch turned on.
As beautiful Caden demonstrates, he's clearly a "C" carrier, with full expression of pigment (melanin):
But what's also true, despite his lighter color, is that Amy G's precious baby, Sully, is also a clear carrier of "C"
Sully's lighter color isn't created by a lack of expression of pigment, but by his chocolate pigment ("bb") being diluted ("dd") to create his gorgeous "Pearl" or "Isabella" coloring. His pigment, however, is fully expressed. (Btw, if Sully was a solid Isabella color, I think we could play "Find that dog!" against the matching leather of his couch.)
Next in our series is a little gene known as "cch." Alone, it has little effect, doubled ("cch cch") it can create a paler shade of tan or red. "cch" has a much greater effect on Phaeomelanin than it does on Eumelanin. In a way, "cch cch" does to Phaeomelanin what "dd" (dilution) does to Eumelanin (black or chocolate). It dilutes the Phaeomelanin pigment that expresses, creating a visibly lighter color. While "cch" has a much greater impact on Phaeomelanin (red or tan) than Eumelanin (black or chocolate), you can sometimes see the subtle effect of "cch cch" in a black dog, whose black color is not quite as dark as its "C" carrying black littermates. This color is known as "Charcoal." And/or, you will sometimes see the effect of "cch cch" in a black or chocolate dog whose tan points have been lightened (cch-diluted) to a very pale shade of cream or near-white.
This is adorable Tucker, and he's a "Charcoal." The "cch cch" factor has lightened his black coat - slightly - and lightened his tan points to cream:
When "cch cch" (double-recessive, or two "cch" genes) meet the double-recessive of "ee," something very interesting happens. "ee" restricts Eumelanin (black or chocolate) from forming in the coat, in totality, but doesn't affect the Eumelanin in the nose leather or eye color, leaving only Phaeomelanin (red or tan) to visibly express in the coat. Then the double "cch cch" comes along to lighten (dilute, although this is not "d" dilution) the existing Phaeomelanin pigment. Without Eumelanin in the coat, and with the Phaeomelanin pigment diluted, we have a pup who at birth who looks as though he or she is nearly absent of pigment all together ("born near white"), but whose color develops slowly over the next several weeks, and then continues to develop throughout the dog's lifetime. This developing color is a cch-diluted shade of red or tan.
Since "ee" only restricts Eumelanin from the coat, but not the nose leather or eye color, we can look to the dog's nose leather and eye color to determine what other color genetics he or she carries:
A dog whose Eumelanin has been restricted from the coat, who is born "white" and who develops its Phaeomelanin (red or tan) color as it matures, and whose nose leather is BLACK, is registered (according to the current standards of UKC) as an "Apricot."
A dog whose Eumelanin has been restricted from the coat, who is born "white" and who develops its Phaeomelanin (red or tan) color as it matures, and whose nose leather is any color OTHER THAN BLACK, is registered (according to the current standards of UKC) as a "Lemon." This means that a diluted black nose ("B/dd"), a chocolate nose ("bb") and an Isabella nose ("bb/dd") are all labeled exactly the same - "Lemon."
According to the current UKC color guide: "LEMON - This is the dilute version of the apricot colors. The only difference between lemon and apricot is that lemon-colored dogs have self-colored nose pigment. Either may be varying shades of orange to lemon."
Please understand that "Lemon" is NOT a "dilute" version of "Apricot." No more than "Chocolate" is a dilute version of "Black."
In a "Lemon" dog, the Eumelanin is simply one of the "non-black" colors, such as "diluted black" (or "B/dd" - "blue"), chocolate ("bb"), or "diluted chocolate" (bb/dd" - "Isabella").
Examples of Apricots and Lemons:
Miss Cookie (How cute is she?!!!) "MicroRatz
Apricot Cookie" owned by Doreen Lester
And here's Melody - all grown up!! If you didn't know she was born a "Lemon" would you have guessed it from her adult pics?
For more information on the "cch cch x ee" factor - see Lesson #6.
It would be a mistake to assume that a white dog is always "cch cch / ee." Other genes, such as those found in the "S-series" can affect the distribution of color, and can create a "white dog." What generally defines a "cch cch / ee" dog is the total restriction of Eumelanin (black or chocolate) from the coat, a white or near white birth (often spots of pale tan coloring are noted at birth), and the development of existing Phaeomelanin (red or tan) pigment as the dog matures.
Yet, the "cch cch / ee" combination can produce an entirely white dog - without coat color, and whose nose leather is either black, chocolate, blue or Isabella, if no Phaeomelanin exists. For example, "ee" restricts the formation of Eumelanin (black or chocolate), if no Phaeomelanin exists, than the dog is left without pigment at all, and will be born and remain completely white.
And finally, we come to the most recessive gene in this series, "c."
According to Burns and Fraser, a dog who is "cc" would have a white coat and blue eyes, however, true albinism is the total absence of pigment in the coat, eye, and nose leather. Therefore, a "cc" albino dog would be pure white in coat, with pink eyes (total absence of pigment), and pink nose leather. Since pigment (or melanin) helps protect our skin from the potentially damaging rays of the sun, an albino dog would require additional protection from the sun and would be prone to skin and eye damage. Fortunately, I am unaware of any albino Rat Terriers at this time.
As stated under "cch," it would be a mistake to assume that an "all white" dogs is an "albino." Albinism is more than a coat absent of color (white), but extends to the entire dog, with the total absence of pigment extending to the eyes and nose leather.
Copyrightę2006 Sue Campbell - All Rights Reserved