Questions: (click to go to the complete question and answer)

 

Q:  I have heard from breeders that chocolate is a dilute. Brown is created by a modification of eumelanin right? so in some sense I can understand why it is sometimes lumped with the diluter gene effects. But if you look at other genetic sites, when they speak of brown, the color brown looks like what our breed calls Chocolate. So where does Brown come in in our breed?

A: You've heard wrong (from other breeders). Chocolate is NOT a dilute. It can BE diluted (Pearl, Isabella), but it is not, in itself, a dilute.

To "dilute" involves the action of the double recessive "d," or "dd" (which we'll discuss in-depth later), in which a color is "diluted." (Think "action.")

"dd" = to dilute.
"bb" = inability to form black.

Two different genes. Two very different actions.

You wrote: "But if you look at other genetic sites, when they speak of brown, the color brown looks like what our breed calls Chocolate. So where does Brown come in in our breed?"

This is a matter of semantics. Some breeds call it "brown," and some breeds call it "chocolate."

Eumelanin = black or brown

Chocolate is not a modification of Eumelanin, but rather the color of Eumelanin when black is unable to formulate. It's still "Eumelanin."

Now, you'll see dogs that exhibit only Phaeomelanin (tan or red) that are, in fact, very "brownish" in color. These dogs have black noses. They are able to formulate black, but the black has been restricted in totality in the coat (but not the skin or eyes) by other genes - which we'll also discuss in-depth, later . These restrictive genes ("ee") permit the coat to only (visibly) exhibit Phaeomelanin (again, the difference between what you can "see," and what is "true, genetically"). This color is also not, in and of itself, a "dilute."

I think the confusion comes in the nose leather. Folks see a chocolate nose and think, "It's lighter - it must be diluted." But it's not been "diluted." Rather the nose leather in a chocolate dog is the color of Eumelanin when black is unable to form.

If you can take anything away from this at this stage of the game, take this to heart: "Chocolate is NOT a dilute." The rest will begin to make more sense as we go further into each of the individual color strings, and what all these color genes DO.

Q:  Okay, so I understand that Chocolate is not a dilute, because it's not diluted black, it's the total absence of black (and that nose color is a good visual tip for that). Right? (A: RIGHT!!) So, is the black gene missing all together in a chocolate dog? Is it super-super suppressed? Or just not there?

A:  Chocolate dogs can't formulate black. It's not that black has been restricted or suppressed, but that they don't have the gene ("B") necessary to formulate the color.

They can, however, express Eumelanin - in totality, it's only that the Eumelanin they express is Chocolate.

Now, there are genes that restrict Eumelanin (we often say "restricts black," which is less clear, because it's really all Eumelanin that's being restricted), such as in the pattern of "Sable." The sable gene restricts Eumelanin, but only in the coat (it doesn't affect eye color or nose leather), and not in totality. Sable restricts Eumelanin (black, diluted black, chocolate) and determines the placement of Eumelanin vs. Phaeomelanin into the unique pattern of sable that we "see."

Sometimes the sable gene creates a dog that visibly appears to express no Eumelanin at all (clear tan), but the dog still carries the gene necessary to produce black "B" Eumelanin (unless it's a chocolate Eumelanin ), the visible expression of this has simply been restricted, in totality. This again highlights the difference between what you "see" and what is "true, genetically." Eumelanin is still there (black, diluted black, chocolate), but it's been "restricted" from view. (We'll go into this a lot more when we study the "A" or Agouti series.)

In Chocolate, however, black isn't there. It's not been "restricted," or "suppressed." It's just not there ("B"), at all. Eumelanin, however, is still there, and completely expressed as the color chocolate.

Then there are other genes that restrict Eumelanin in totality (but again, not in the nose leather or eye color) "ee." Again, these dogs would visibly appear to have no Eumelanin, at all, but they still carry the genes to produce Eumelanin, and if they carry "B," they have the ability to formulate black, it's simply been restricted. Looking at the nose leather tells us whether they carry Black Eumelanin, Diluted Black Eumelanin, Chocolate Eumelanin, or Diluted Chocolate Eumelanin (Pearl, Isabella), even when these "colors" have been completely restricted from the coat.

Q:  So my male Pearl Tri is a chocolate dog which has been diluted to pearl. Basically? In my currently way over-simplified understanding?

A:  Not over-simplified at all - you got it .

"Blue" is "Black, Diluted" - or "Diluted Black."

"Pearl" (or Isabella) is "Chocolate, Diluted" - or "Diluted Chocolate."

And you're right again about the nose leather. The nose leather is our clue to what the dog carries, when the coat fails to tell us the full story. We can tell from the nose leather whether the dog carries "Black Eumelanin," "Diluted Black Eumelanin (blue)," "Chocolate Eumelanin," "Diluted Chocolate Eumelanin (Pearl/Isabella)," etc.

 

 

(Next Lesson: The "A" or "Agouti" color string series) -  Back to Breeder's Message Board

Copyrightę2006 Sue Campbell - All Rights Reserved