Rocky and Rusty

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Rat Terrier - Canine Color Genetics
Lesson #3 - "B" Series

By Sue Campell, SouthPaw,

Lesson #1 (Introduction), Lesson #2 (A-series), Lesson #4 (C-series), Lesson #5 (D-series)
Lesson #6 (E-series)

The B Series

In the "B-series" we're only dealing with two genes. That makes it nice and easy. Even better, there's a simple dominant to recessive in play: "B" is dominant, requiring only one "B" gene to formulate black. "b" is recessive, requiring two "b" genes ("bb") to produce what we call "Chocolate."

Some breeds call Chocolate, "Red," or "Tan," but we've already learned that true tan and red is produced through Phaeomelanin, and when we're talking about the "B" series, we're only talking about Eumelanin.

Lynn Pinkey's stunning pup, Shevaun - Cruzin' Kennel
bred by IrishGlyn

Some of the older Rat Terrier pedigrees will list a chocolate dog as a "Tan," or a "Red." When I first purchased Cracker Jack, a beautiful high red chocolate Rat Terrier, his papers had him listed as a "Tan & White." That was only seven-and-a-half short years ago. It's easy to understand the confusion. When you look at beautiful Shevaun's richly colored tan points above, imagine a dog entirely of that color. Or look again at Tammy Jordan's beautiful Red Sable boy in Lesson #2 (under Dominant Recessive ay), with so much restriction of black in his coat, and his deep, deep mahogany Phaeomelanin, it can get confusing. Lucky for us, the nose knows.

Later in this lesson, we'll discuss the many colors of chocolate: from pale brown to deep liver. When we realize that Phaeomelanin also produces a wide variety of color: from pale gold to rich mahogany, it's easy to understand why people were once so confused.

Dominant B

The "B" gene (or allele) is the dominant gene in this series. "B" allows the formation of Black pigment in the coat and nose leather. It also permits darker eye pigment.

Often, "B" will be referred to simply as "Black," but when you look at the colorful group of dogs below, all of whom have the dominant "B" allele, it's easy to understand why the definition of "Black" doesn't quite cut it. Having the "B" gene doesn't necessary mean a dog will BE Black. What it means is that the dog has the ability to formulate or produce Black pigment. There are other genes, in other color series, that can restrict or affect what is visibly produced, or what we "see." It's also important to remember that the "B-series" only affects Eumelanin.

Because "B" is the dominant allele in this series, only one "B" gene is necessary to produce a dog who can formulate Black. So a dog who is "BB" may look identical to a dog who is "Bb." The "Bb" dog would "carry chocolate in the recessive," and be capable of producing "bb" offspring when paired with another dog carrying "b." But visually, the "BB" and "Bb" dog may appear exactly the same.

Dogs who are visibly "B." Notice that the first three exhibit black noses. The fourth does not:

Black & White

GR CH RPK's Crystal Image

Don't you wish you knew what Crystal was looking at? Such a gorgeous picture of a beautiful Rat Terrier

Black, White, Tan

Carol Rieger's GR CH Dragonfly's New Kid In Town - "Zander"

Beautiful and regal Zander. Any question this dog is able to formulate black?

Tan Sable & White

Carol Rieger's Dragonfly's ItzaTanZan Pooch - "Norah"

Now take a look at Carol Rieger's beautiful Norah, above. Norah exhibits very little, if any, black in her coat, but her black nose leather and dark eyes tells us she's a "B_", and a cute one at that!! The nose knows. (Carol, if you ever need to find this girl a home, you just give me a call.) J

Dogs who are "Diluted Black," or more commonly referred to as "Blue," are also "B" ("B_/dd"). In order to achieve dilute black, the dog must be able to formulate Black Eumelanin. Take a look at Carmeta French's sweetheart of a girl, Cyan. Her Black Eumelanin is diluted to Blue by recessives in the "D-series," and her nose also tells us she has the dominant "B" allele, but in its diluted form. Her eye color is also diluted:

Blue, Tan & White

3b's Ragtime Blus @ Warren Mtns - "Cyan"

Recessive b

The "b" gene is the recessive gene in this series. Dogs who have the double recessive of "bb" can't produce Black pigment.

This inability to formulate black extends from the coat to the nose leather and eye color. This affect is often referred to as "self-colored."

The "B-series" has no affect on Phaeomelanin, and affects only Eumelanin. Notice that the tan points remain unchanged.

The "b" gene is not a dilute, and dilution is not its action. There seems to be a great deal of confusion over whether Chocolate is a "dilute." Dilution comes from the "D-series" and has absolutely nothing to do with Chocolate. Chocolate can BE diluted (Pearl or Isabella), just as Black can be diluted (Blue), but Chocolate, itself, is not a dilute. For more on this subject, see the FAQ.

Chocolate is simply the inability to produce Black pigment. This doesn't mean that the dog doesn't produce Eumelanin, but that without Black pigment, the Eumelanin is Chocolate.

Dogs who are visibly "bb" (all exhibit self-colored eyes and nose leather):

Chocolate & White


Chocolate, White & Tan

Stacy McWilliams -

When the sable gene is involved, the Eumelanin hairs are restricted, but not in totality, creating the "sable pattern."

What we typically see as "Black hairs" in the Tan Sable, are "Chocolate hairs" in the Chocolate Sable.

For many years people argued that "Chocolate Sable" wasn't possible. Why they believed this, I don't know. But in the Chocolate Sable dog you'll see Chocolate hairs (which may be very light chocolate or very dark chocolate, depending on the polygenes attached to the "b" genes) sabled throughout a Phaeomelanin base.

When you learned about the "A-series," you learned that sable means "Dominant Phaeomelanin." When the colors in Phaeomelanin can be so close to the colors in Chocolate Eumelanin, as we saw earlier with Lynn Pinkey's beautiful Shevaun, it's understandable why the Chocolate sable hairs can be more difficult to detect or to differentiate from the Phaeomelanin (or tan) coat.

The Chocolate Sable dog, like all "bb" dogs, has a self-colored nose. This is often the determining factor in knowing whether a sable dog is "B_" or "bb."

Elsie Killen's girl, Macy, below is a splendid example of a Chocolate Sable. When you look at the Eumelanin hairs in Macy's coat (the sabled hairs), it becomes evident that Macy would have been a very dark chocolate color, if the "ay" gene wasn't in play (restricting the Eumelanin in the coat, but not in totality). The sable hairs in Macy's coat look almost black, but they're not, they're a very dark chocolate color. Her nose leather is appropriately self-colored to match her coat, and her beautiful light eyes take in the world and seem to beg attention.

Chocolate Sable & White

Elsie Killen - CH Killen's RPK Macy

"Diluted Chocolate," more commonly referred to as "Pearl" or "Isabella" (and sometimes given the misnomer of "Blue Fawn"), is also "bb." In order to achieve diluted Chocolate, the dog must be 1) unable to form Black pigment, and 2) the Chocolate Eumelanin must be diluted by the double recessive of "dd," from the D-series.

A Chocolate dog, alone, is NOT a dilute, but Chocolate can BE diluted. This dilution also affects nose color, producing nose leather that is "diluted chocolate," or "self-colored," with diluted eye color. Take a look at Electra Blair's honey of a Pearl:

Pearl/Isabella & White

(Hey Electra, let me know this beauty's name and whether he/she has tan points J)


The Nose Knows

When in doubt, nose leather can be a good indicator of what a dog has in its color genetic string. The nose knows:

(Black, Blue [diluted black], Chocolate, and Pearl [diluted chocolate]- in that order)

It's important to understand that "self-colored" noses, such as those in "Blue," "Chocolate," and "Pearl/Isabella" mean just that: "self-colored." A lighter chocolate dog will have a lighter chocolate nose. A darker chocolate dog will have a darker chocolate nose. And so on... the perfect nose leather to match the perfect coat color... whatever that may be.

Many Shades of Chocolate

All chocolate lovers know that Chocolate Rat Terriers come in a variety of shades and depths of color, from pale brown to deep liver. These shades of color are determined by rufus polygenes attached to individual "b" genes (or alleles), and not part of any documented Color Series that we can follow. Fortunately, the depth of color that you SEE, visually, tells you what rufus polygenes are attached - be they light or dark. Typically, a Chocolate Rat Terrier can only produce offspring as dark as the darkest dog in the pair. Lighter offspring can be produced, but usually this is due to other genes, such as "ayat" making a Chocolate dog sable, which restricts the amount of Chocolate Eumelanin that you see.

The many shades of Chocolate:


Elsie Killen's Many Shades of Chocolate

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