Explain coat color genetics - The Horse Forum
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post #1 of 5 Old 03-01-2014, 05:30 PM Thread Starter
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Explain coat color genetics

Ok, I know this can get very complicated and in-depth, but could someone just give me a basic rundown of coat color genetics? I've looked at different websites but it's hard to understand and if I have questions I can always ask here/respond to posts :)
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post #2 of 5 Old 03-01-2014, 07:44 PM
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The basic coat colors of chestnut, bay, brown and black horses are controlled by the interaction between two genes: Extension (gene symbol E) and Agouti (gene symbol A). The Extension gene (red factor) controls the production of red and black pigment. Agouti controls the distribution of black pigment either to a points pattern (mane, tail, lower legs, ear rims) or uniformly over the body. The effects of approximately 10 other genes may modify these pigments to provide an array of colors in the domestic horse ranging from white to black.
The basic colors can be diluted by at least five genes: Cream, Champagne, Dun, Pearl and Silver. The Cream gene has a dosage effect in that a single copy of Cream produces palominos, buckskins and smoky blacks. Two doses of Cream produce cremellos, perlinos and smoky creams. Pearl is recessive; two copies of the gene or one copy of Pearl and one of Cream, are needed to see the dilution effect on the coat color. Champagne, Dun and Silver do not show a dosage effect.
There are several genes responsible for white patterns on horses. White spotting patterns on the base coat color are produced by the Dominant White, Appaloosa, Tobiano and Overo genes or as mixed white and colored hair patterns produced by the Grey (progressive whitening with age) and Roan genes. Several genes are involved in the production of white spotting patterns known as overo. Among those, the gene responsible for the frame-overo pattern is associated with a lethal disease of newborn foals called Lethal White Overo foal syndrome.
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post #3 of 5 Old 03-01-2014, 08:52 PM
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I always thought this was a fun little tool for grasping the basics:

Horse Coat Color Genetics: An Introduction
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post #4 of 5 Old 03-01-2014, 09:46 PM
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Assuming you understand the basics of genetics (genes/alleles)

All horses are either black or red.

There is the agouti gene that can only be seen on black horses since it restricts the black to the points making bay or brown. (On red there is no black to restrict)

Those are your 4 basic colors.

Then you have the modifiers. They change the color into something else.

Some are stronger with two genes. For example. Dun with change any color into color + dun. ("Dun" being the traditional bay + dun, then "Red Dun" for chesnut + dun the confusing part is often different colors have several names or people mistake the color for another, or you can have several modifiers on one horse! "dunalino" dun + palomino (cream + chestnut) but that's getting ahead of ourselves..)

Cream is an example of a modifier that is stronger with two copies.
black + cream = smokey black + another cream (black with two cream genes) = smokey cream
bay/brown = buckskin = perlino
chestnut = palomino = cremello

Interesting how some "normal" colors are so closely related to "rare" colors.

There are several modifiers, there are also modifiers that effect only a certain color (similar to agouti on black) for ex, silver will only show on a black horse. Or there are other modifiers (aside from the main ones, more specific) such as flaxen that only show on red (you don't hear "flaxen black" do you?)

I would say the common ones are cream and dun, occasionally silver depending on the breed. Others are rather recently discovered and not completely understood (though you can argue we don't completely understand a lot of science!).

There is grey, which acts like a blanket, and will slowly turn whatever color horse white as it ages. (If the horse was black it is still genetically a black horse! The genetic color NEVER changes! It is a black horse with one or two grey genes).

Then of course there is the leopard pattern (Appaloosas) and pinto patterns, but that is a whole other ball game and I think not what you were asking. Also, you need to learn to stand before you run

Love this book: Horse Colour Explained by Jeanette Gower | eBay (I don't remember what I paid but it was NOT $60! I'm sure you can find it elsewhere.)

Morgan Colors- Smoky Black Morgan Horses
Equine Color Genetics

Some good for basics websites.
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post #5 of 5 Old 03-01-2014, 09:47 PM
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Definitely feel free to ask specific questions :)
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