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Monday, June 4, 2012

Dilutions I: Cream in my coffee, sugar in my tea: Why Palominos and Buckskins cannot be breeds.

Dilutions I: Cream in my coffee, sugar in my tea: Why Palominos and Buckskins cannot be breeds.

by Dainelle Kinsel
I wasn't sure which dilute genes to start with, but I've seen lots of books and websites make the mistake and call palomino horses a "breed" so I figured I would start here. <smiles>
Cream (or creme) is the first of many modifiers that work to change the way phaemelanin (red pigment) and eumelanin (black pigment) ultimately look. (This is also known as a phenotype. Genetically, a chestnut horse is ee but it's phenotype is one of many shades of red.)
Cream is an odd gene. It is known as an incomplete dominant which means it affects the end color differently whether a horse has one dose or two. The other modifiers, such as sooty and panagre also affect these colors, just like chestnut, black and bay.
Remember! All horses are genetically black or red. Anything else a modifier that affects the ultimate outcome of those two colors.
That said, let's look at how cream affects the base colors. 
This little table comes in handy: (I've abbreviated the genetic code down to what's important in this case:)
A chestnut horse with one "dose" of cream is a palomino. (ee Crcr)
A chestnut horse with two doses of cream is a cremello. (ee CrCr)
Palomino horses have dark skin. Their bodies may range in shade from cream, yellow, gold, etc, to sooty or "black gold" based on the other modifiers present. Their manes and tails can range from flaxen to cream to pure white.
The cremello horse has pink skin, nearly white points and often blue eyes. If it's skin is dark, it's not cremello.
A bay or brown horse with one dose of cream is buckskin. (A- E- Crcr or At- E- Crcr)
A bay or brown horse with two doses of cream is perlino. (A- E- CrCr or At-E- CrCr)
Buckskin horses have dark skin. Their bodies may range in shade from cream, yellow, gold, etc to sooty or even "off black" based on the modifiers present. Points are black. Some may have a "counter shaded" stripe on their backs, but this is not  a dorsal stripe.
The perlino horse has pink skin, points that look about one shade darker than the body, and eyes that are often blue.
A black horse with one dose of cream is smoky black. (aa E- Crcr) (Which doesn't look any different than a black horse without the cream gene.)
A black horse with two doses of cream is smoky cream. (aa E- CrCr)
Smoky cream looks like a cremello horse that's had light ink poured all over it---ok, that's confusing, so let's stick to the working definition: looks sooty on top of cream (cinnamon on whipped cream perhaps?) and often has blue eyes.
What's important here is to notice how the presence of the cream gene affects the base color: a smoky cream horse is almost ghost-like and looks completely different to the naked eye than a smoky black. Buckskin and perlino seem to be on opposite ends of the color scale, as do palomino and cremello. Cremello and perlino have often been referred to as "white" while smoky cream has been misidentified as "white" "light dun" and even "grey." So, this is why is a wonderful thing that so many registries are finally getting around to wanting their horses DNA tested. We have learned so much in such a short amount of time---and there is still lots more to learn.
On all of these dilutes (palomino, buckskin, perlino, smoky black, and smoky cream: pinto and appy patterns, as well as face and leg markings are easy to see!)
But let's get back to the subject at hand!
Let's also take a moment to understand that horse colors seem to stack (in my opinion.) It is entirely possible to have a horse that is a brown buckskin tobiano or a smoky cream spotted blanket. When we take the time to write out the colors properly, everyone can understand---from the registrar to the lay person. Hopefully one day descriptions like "a tricolored horse" will fall by the wayside. We can only hope!
Alright then--so just why can't palominos or buckskins ever be a breed or breed true? (Breeding true means if you breed two palominos you get 100% palomino. Well, you can't. I'll show you why...)
As we saw above, there is no such thing as a "palomino" or "buckskin" gene. These colors come about through the work of the cream gene acting on the black or red base color.
So let's do some virtual breeding:
Let's take a palomino stallion (ee Crcr) and breed him to a palomino mare (ee Crcr).
And since this is virtual, we don't have to wait ten months. We have a foal.
What color do you think it will be? (no cheating!)
Well, if you said palomino, you are 50% right. You also have a 25% chance of a cremello foal and 25% of a chestnut foal.
Wow! So, then you understand that palomino doesn't breed true. (You may give yourself exactly one pat on the back. Don't want you too get too smug...yet...)
In other words, when you cross those two golden bombshells, the Punnet Square will look something like this (I omitted the "ee"s since it's understood both horses have them...)
        Cr       cr
Cr  CrCr     Crcr
cr   Crcr      crcr
CrCr- cremello (two doses of cream)
Crcr- palomino (one does of cream)
crcr- no doses of cream
It works the same way for buckskins. This is why chestnuts are important in breeding programs for palominos, such as ASBs. It gives about a 50/50 chance of getting either palomino or chestnut, no chance of cremello.
Now, if you really wanted to produce palomino foals 100% of the time, you would take and cross cremello with chestnuts!
Ok, I think the coffee is cold now and I need some lemon for this iced tea. Stay tuned for the next part of the dilution discussion: dun--the cowboy color.

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