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Horse Coat Colour

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by

Alanna DiCiocco

on 17 November 2013

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Transcript of Horse Coat Colour

Horse Coat Colour Genetics
By: Alanna DiCiocco


Coat Colours
In 2007 the equine genome was completed. This opened doors to allow geneticists to identify mutations of the basic coat colours. This also allowed them to identify the genes for other coat colours such as spotting patterns.
Genetics
Base Colours
Horses have 3 base coat colours being; bay, chestnut, and black.
These 3 coat colours are controlled by the interaction of the Extension gene and the Agouti Gene.

The Extension Gene controls the production of red and black pigment. Can either make the skin and hair black, or make just the skin black, chestnut or not a chestnut. (gene symbol E). Black being present in the fur is dominant, while no black fur is recessive.

The Agouti Gene controls the distribution of black to either points, or uniformly over the body (gene symbol A). Points are dominant, while all black is recessive

Bay Horse
Will have the phenotype EE or Ee and AA or Aa
The black pigment is present in the hair from the extension gene, and the agouti gene will restrict the black to points (legs, tail, mane, mussel, and ear tips).

Chestnut
Will have the Phenotype ee and AA or Aa or aa
The horse will not have black fur since the extension gene restricts it to the skin.

Black Horse
Will have the phenotype EE or Ea and aa
The black pigment is present in the hair from the extension gene, and the agouti gene has no restrictions of the black.

Dilutions
Cream Dilution- expressed as CR
Causes a loss of pigment in cells expressing brown or red pigment. The gene is dominant and if two copies are present, then the horse appears almost white.
Chestnut with 1 Cream Dilution- Palomino, with 2 cream dilutions- Cremello
Bay horse with 1 Cream Dilution- Buckskin, with 2 cream dilutions- Perlino
Black horse with 1 Cream dilution- Smokey black, with 2 cream dilutions- Smokey Cream

Palamino
Cremello
Buckskin
Perlino
Smokey Black
Smokey Cream
Pearl
Expressed as Prl, Pearl is a rare dilution that resembles the cream dilution and was once called the ‘apricot gene’. It is a recessive gene and only appears on horses that are homozygous recessive for the extension gene (ee). So only chestnuts. On horses that have 1 cream dilution, the presence of the pearl dilution can enhance the dilution even more.
Champagne Dilution
Expressed as Ch, champagne is a dominant gene that dilutes hair from black to brown and from red to gold. The gene can also produce a flaxen mane and tail.
Chestnut with Champagne Dilution- gold colour (gold)
Bay horse with Champagne Dilution- tan body with brown points (Amber)
Black horse with Champagne Dilution- darker tan body with brown points (classic)

Chestnut Champagne
Amber Champagne
Classic Champagne
Silver Dilution
Silver Dilution-expressed as Z
Only acts on black pigmented horses (does not affect chestnuts). Seen predominantly in the Rocky Mountain Horse breed. The mane and tail lighten to flaxen of silver-grey.
Black horse with silver dilution- will turn chocolate coloured
Bay horse with silver dilution- black points and the body will be lightened

Black Silver
Bay Silver
Dun Dilution
Dun Dilution- expressed as Dn
Is a unique dilution that shows “primitive markings” consisting of dark dorsal stripes, shoulder stripes, leg stripes, and sometimes markings on forehead. Like Roan the mutation is still unknown so it is hard to pinpoint.
Black horse with dun dilution- Grullo
Chestnut horse with dun dilution- Red Dun
Bay horse with dun dilution-Yellow Dun

Grullo
Red Dun
Yellow Dun
Pinto Horses
Tobiano- expressed as TO
Responsible for the white patches that occur in the bodies of horses. The gene is dominant and can show over any horse colour. The horses generally have dark coloured heads with white legs and white patched over the topline. The white patches are generally ovals or round patterns.

Overo- expressed as O
Like tobiano it causes white markings on horses. Unlike tobiano, oveor never crosses the midline of the back and it looks like the horse is splashed up from the belly. The horse’s faces are usually white/bald. The gene is also dominant however, horses with two copies of the overo gene are born completely white with multiple developmental defects resulting in death soon after birth.

Sabino- expressed as SB1
Is a subclass of overo and is prized by breeders. It is a dominant gene that causes white to appear on the lower legs, belly, and face. A horse with two copies of the gene will be almost completely white with small amounts of colour.

Dominant White- expressed as W
Is a dominant trait, similar to a horse with two sabino genes. The horse will be almost completely whit with small amounts of colour around the ears and eyes.

Appaloosa- expressed as LP
Also known as the Leopard Complex. The expression includes 3 main components: white spotting, progressive roaning of pigmented areas with age and pigmented leopard spots. The gene is an incomplete dominant, so horses with one copy of the gene are typically a different colour than a horse with two copies of the gene. The leopard complex can range from not showing to extreme white patterning.
There are 3 types of appaloosas: Leopard, Blanket, and Varnish
Leopard Appaloosa
Blanket Appaloosa
Varnish Appaloosa
References
1. University of California, Unknown. "Horse Coat Color." Horse Coat Color. N.p., 2012. http://www.vgl.ucdavis.edu/services/coatcolorhorse.php
2. Larson, Erica. "Equine Coat Color Genetics 101." TheHorse.com. N.p., 13 Apr. 2013. http://www.thehorse.com/articles/31651/equine-coat-color-genetics-101
3. University of Kentucky, Unknown. "Horse Genome Project - Coat Color Genetics." Horse Genome Project - Coat Color Genetics. N.p., 20 Dec. 2011. http://www.uky.edu/Ag/Horsemap/hgpcoatcolor.html
4. Animal Genetics, Inc., Unknown. "LWO - Lethal White Overo Testing." LWO - Lethal White Overo Testing. N.p., 2013. http://www.horsetesting.com/LWO.htm

THE END
Genetics
3 combination of genes
Homozygous Dominant (AA)
Homozygous Recessive (aa)
Combination heterozygous (Aa)
The dominant trait will always show over the recessive. The recessive will only show if it is homozygous (ex. aa, ee,)

Gray Horse
Gray horse- expressed as G
The gray gene causes a progressive depigmentation of the hair, which can result in a coat colour that is completely white by ages 6-8. A grey can be born any colour then begin to show white hairs mixed throughout the body. The gene is dominant.

Gray
Roan
Roan horse- expressed as R
The roan is similar to the grey but instead of lightening over time, they retain dark heads and legs. Researchers have not yet identifies the exact mutation that causes roan but believe it is linked to pinto horse genetics.

Roan
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 (3, unknown)
Pinto refers to the pattern of white that appears on horses, and is different from Paint which is a breed which shows this trait. The pattern is very specific and distinct from appaloosa (which will be discussed soon). There 4 main genes that express this trait
Pearl
Appaloosa
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