Equine Color Genetics
Equine genetics are fascinating, but they can be confusing to decipher, even if you’re familiar with genetics or horses. The purpose of this guide is to simplify the inner workings of horse color genetics with some up-to-date, legitimate sources to back up the information and some photos of real horses so you can identify them “in the wild”…or so you can paint more realistic model horses!
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Special thanks to the following sources: The International Champagne Horse Registry, The Colorful Chincoteague, Morgan Colors, Shining C Grulla Horses, and the Equine Color Genetics group on Facebook.
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Disclaimer: None of the photos on this page belong to me, but they all link back to their original sources. I have gone to great lengths to avoid unsourced photos reposted to Pinterest, etc. whenever possible and not have not cropped any watermarks. Please click the photos to visit the original source for additional photos/information. My intent is solely educational, but if you see one of your photos that you would like removed, please contact me.
{Last updated 6/24/19}
Basic Genetics
If you’re already familiar with basic genetics, feel free to skip this section. In case you’re not familiar with genetics, I’ll provide a crash course based on the principles of Gregor Mendel, the father of genetics. He studied pea plants and the characteristics that they pass on to their offspring (color, height, appearance, etc.), so let’s start with that example. Each characteristic is controlled by a gene, a section of DNA. Each gene has different versions, called alleles. In the pea plant example, the gene for color is controlled by yellow and green alleles. Some alleles are expressed preferentially over other alleles, called dominant and recessive traits. We describe the alleles using letter abbreviations, with dominant traits designated by capital letters and recessive traits with lowercase letters. For example, we’ll use the letter “A” for pea color. If yellow is the dominant color and green is recessive, the yellow allele will be A and the green allele will be a.
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Organisms receive one allele from each parent, so the possible combinations a pea plant could have for color are AA, Aa, and aa. We call these combinations “genotypes”, or the genetic description of the genes an organism has. Since yellow color (A) is dominant, any genotypes with an A will appear on the organism as yellow (AA and Aa). We call the appearance of the gene a phenotype. The only way to get a green phenotype is to have the genotype aa.
If a genotype has two of the same allele (AA or aa), we call that homozygous. That means the organism has a 100% chance of passing down that allele to their offspring. If the genotype has two different alleles (Aa), then the organism can only pass on the A or the a to its offspring; there is a 50% chance of passing each allele on. We call this heterozygous.
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If we know the genotypes of the parent pea plants, we can predict what their offspring will look like using a diagram called a Punnett Square. We put one parent’s alleles across the top and the other parent’s alleles down the left side.
Each square is filled in with the allele from the top and the allele from the left side, with the capital letter (dominant allele) first. The four results are the four different possibilities of the offspring. In the AA x aa example, all the results are Aa, so there is a 100% chance that the offspring will have the yellow phenotype.
In the Aa x Aa example, there is one AA result, two Aa results, and one aa result. This means there is a 75% chance the offspring will be yellow and a 25% chance they will be green.
You can also make larger Punnett squares using multiple genes. For example, if we use T for tall plant height and t for short plant height, we could predict the height of the offspring using the parents’ alleles along with the color alleles. We could cross AaTt (heterozygous tall yellow plant) with aatt (homozygous short green plant) using a 4x4 Punnett square. Try it!
Chestnut, Bay & Black
Chestnut
The incredible rainbow of horse colors is all based on black, bay, and chestnut. These three colors are controlled by two genes called Extension and Agouti. The Extension gene (E) controls red and and black pigment. If a horse has the genotype EE or Ee, they will have black skin and black hair. If they have the genotype ee, the black pigment will be limited to the skin and the hair will be red (chestnut). The term “sorrel” is synonymous with chestnut, but is somewhat ambiguously used by some breed associations (like AQHA) in addition to "chestnut". Red foals are often born with salmon-colored skin and shell-colored hooves (even on legs without a white marking), both of which will darken with age. There are many different shades of chestnut that cannot be fully explained by genes.
Liver chestnut: a dark, purplish shade of chestnut
Black chestnut: a shade of chestnut so dark that it appears black
Secretariat aka "Big Red", chestnut Triple Crown winning Thoroughbred stallion.
An unnamed black chestnut mare. She was born red and darkened over time, but is still genetically chestnut.
Hang N Grace Under Fire, a liver chestnut Morgan mare. Confirmed eeAa.
Chestnut horses can sometimes have a blonde mane and tail, called flaxen. Flaxen appears to be recessive, but has not been mapped to a specific gene. The flaxen modifier only acts on chestnut pigment and seems to require two copies for expression. Although bay and black horses can carry the flaxen gene, only red-based horses can express it. A light mane and tail on bay- and black-based horses is caused by the silver gene (discussed later), not flaxen. Flaxen chestnuts can also be confused for dark palominos (discussed later).
Surfer Dude's Riptide, a flaxen liver chestnut Chincoteague Pony stallion.
Samant, a flaxen chestnut Marwari stallion.
Heaven's Angel, a flaxen black chestnut mare and her palomino colt. She was suspected to be black silver dapple, but testing revealed she is red-based.
A team of flaxen chestnut Percherons pulling a carriage tour on Mackinac Island.
Bay
The Agouti (A) gene controls the distribution of black pigment in the horse’s hair and works together with E to determine coat color. AA or Aa confines the black pigment to the points, causing a bay coat, but only if the horse also has an E allele. If the horse is chestnut and only has the ee alleles, Agouti has no effect on phenotype, but can be passed on to offspring. There are many shades of bay, but the variations have not yet been mapped by genetics.
Wild bay: very limited black pigment along the topline and on the legs.
Seal bay: very dark bay with cinnamon-colored muzzle and sometimes stifle and underbelly.
*a test was developed for the theoretical brown/seal bay gene (called At, for black & tan) but subsequently pulled from the market due to inconsistent results. At is considered disproven. Seal bay is simply a variation of bay.
Mealy bay: any shade of bay with heavy pangare. More common in draft breeds and ponies.
Brown: usually refers to an overall dark bay coat, but can sometimes mean the same as seal bay.
Blood bay: a very red-toned bay.
Afleet Alex, a bay Thoroughbred stallion.
A 2001 Harlan's Holiday x Sophie's Trophy TB filly in wild bay. Note the lack of black pigment on the legs and along the topline.
American Pharaoh, bay Triple Crown winning TB.
Medaglia D'Oro, a bay TB stallion registered as brown.
Seattle Proud, a seal bay son of Triple Crown winner Seattle Slew. Note the cinnamon muzzle.
Legendary Design, a blood bay TB stallion. Note the red undertones in his coat compared to the other bay examples.
Chestnut and bay horses often exhibit a trait called “pangare” that causes a light tan “mealy” color on certain points of the body, usually the muzzle, eyes, underside, and stifle (the area in front of the knee on the belly). Pangare can affect any color, but it is most obvious on chestnuts and bays. It has not been mapped to a gene yet. Primitive breeds like the Exmoor pony and wild horses like Przewalski’s horse show this characteristic well.
Exmoor Ponies exhibiting mealy muzzles and eyes.
A wild Przewalski's horse with mealy muzzle and underside.
A flaxen chestnut Belgian Draft with pangare shading.
Black
A horse that is homozygous recessive for Agouti (aa) will not have the black pigment restricted to the points, so it will be completely black if it also carries EE or Ee. However, a horse that is homozygous recessive for Extension (ee) will remain chestnut since the Agouti doesn’t have any black pigment to act on. This means that a black foal is not possible if at least one parent is bay (Aa or AA).
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If a black horse is left in the sun, they can become “sunburnt” and fade into shades of brown with reddish manes and tails that can be confused for bays or even chestnuts. However, the hair will grow back true black.
Alysh-Dagley, a black Akhal Teke stallion.
Carltonlima Emma, Queen Elizabeth II's beloved black Fell Pony mare.
M R Innovated, a sun-faded black AQHA colt.
Breed Spotlight: Friesian
Friesians are known for their black color, meaning almost all individuals must be EEaa (homozygous dominant for black, homozygous recessive for Agouti). However, Friesians are very rarely chestnut. How could this be possible from two black parents? Imagine a Punnett Square with two parents heterozygous for black and homozygous recessive for Agouti (Eeaa). There would be a 25% chance that the offspring would inherit an e from both parents, causing a chestnut phenotype and an eeaa genotype. Unfortunately, chestnut Friesians are not recognized by breed associations and stallions carrying the Ee alleles are not allowed to be registered, meaning that one day there will likely be no longer such thing as a chestnut Friesian.
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Sjoerd, the most decorated Friesian stallion in the world.
Fire Magic, a rare chestnut Friesian stallion.
Cream Dilution
A gene called “cream” can dilute any of the basic colors: chestnut, bay, or black. The cream gene (Cr) behaves with incomplete dominance. An example of incomplete dominance is the snapdragon flower. If red color is dominant (R) and white color is recessive (r), then a cross of RR x rr with incomplete dominance means that an offspring with genotype Rr will be pink (red + white) rather than expressing only the dominant allele (red).
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The cream gene is dosage-related; two copies of the gene will strengthen its effect on the coat color (unlike black, where EE and Ee are both the same level of blackness). Think of the cream gene as adding cream to coffee – the more cream, the lighter the coffee becomes.
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One copy of cream is designated nCr, with n to represent the lack of a second copy of cream. Cream generally turns red body color to gold and red manes/tails to cream. One copy of cream can not affect eumelanin (black pigment), meaning that smoky black horses will look identical to non-cream blacks and that the points on buckskins remain black instead chocolate brown. This means that the skin color of single-cream horses will still be black. Shade differences between black horses and smoky blacks can often be attributed to the relatively recently-discovered nd1, interaction with the silver gene, fading, or mineral imbalances. Cream is present is most breeds.
Black + Cr = smoky black -- looks identical to black; faded black may be confused with liver chestnut
Chestnut + Cr = palomino -- Can be confused with flaxen chestnut
Bay + Cr = buckskin -- Can be confused with dun
Triple S Silver Smoke, a smoky black Morgan colt. Sun-faded (left) and non-faded (right). Confirmed Ee/Cr.
Misty Moon Dancer, a smoky black tobiano Chincoteague Pony mare.
HP Aphrodite, a smoky black Gypsy Vanner filly with faded mane (left) and non-faded (right).
Noah's Shadow, a severely sun-faded smoky black Chincoteague Pony mare. The light inner ears suggest nd1, which makes horses more prone to fading.
Goldhills Make My Day, a dappled light palomino Welsh Pony (Section B) gelding.
Eyarth Rambo, a palomino Welsh Pony (Section B) stallion.
Gunther, a palomino Drum Horse stallion.
Season's Miss Effie, a palomino Morgan mare and her buckskin filly.
The Bronze Promise, a buckskin Morgan stallion.
Aktepel, a buckskin Akhal Teke mare.
Taskin, a buckskin Gypsy Vanner stallion. Confirmed Ee/Aa/Cr.
Freedom's Jolie Prize, the only known buckskin Shire in the world. Confirmed EE/Aa/Cr.
A characteristic that often affects palominos and buckskins (but can affect many other colors) is the “sooty” or “smutty” coloration. Soot appears to have a genetic component, but it has not been genetically mapped yet. It causes black countershading along the topline, shoulders, rump, and face, making the horse look like it has had soot dumped on it. Sootiness is progressive; the extent of soot can spread from topline downwards as the horse ages, and can change with the season.
Sootniess can create some really spectacular dapples, make a palomino look chestnut, or even produce a pseudo-dorsal stripe on horses that do not carry the dun gene (discussed below). It can also cause grey-silver manes or tails on flaxen horses if the soot is especially concentrated.
Sheherezad, a sooty buckskin Akhal Teke mare.
Pamel-Kan, a dappled sooty buckskin Akhal Teke stallion.
Misty's Twist O Mist, a sooty palomino Chincoteague Pony mare. This is the same horse photographed 6 years apart. She might be called a "chocolate palomino" for obvious reasons.
Tinsel Jac, a sooty palomino AQHA stallion. Note the pseudo-dorsal stripe and dark mane.
Heathermoor Gold Banner, a (very) sooty palomino Morgan gelding. He started life as a normal palomino and progressively became more sooty until he could pass as a liver chestnut or dark bay.
Farceur's Golden Angel, a sooty palomino Morgan mare. Note how the soot is limited to mostly the mane.
Metigoshe Mariah, a sooty palomino Morgan filly. Confirmed ee/nCr. As a yearling (middle), she could be mistaken as a silver bay. Her dam was a black chestnut, suggesting a link between very dark chestnuts and extreme sootiness.
SC Island Centavo, a sooty buckskin Morgan gelding. Confirmed EE/Aa/nCr.
Dutch, a chestnut KWPN gelding. He displays a very peculiar sooty phenotype that is concentrated along his dorsal and ventral lines. Note his dark mane and tail, which have caused him to be mis-identified as a bay; however, the complete lack of black points on his legs and head prove he is a chestnut. The dark spots on his left rump are called Bend-Or spots. (photos courtesy of Leigh T.)
Double Cream Dilution
Two copies of cream (CrCr) makes the horse’s skin pink, the eyes blue or bluish green, and makes the body hair a creamy color. The undertones of the cream depend on how light/dark/red/mahogany/etc. the base coat would be without the cream. The exposed pink skin around the muzzle and eyes often becomes mottled over time when exposed to the sun due to increased melanin production.
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Horses with two copies of cream are commonly called “double-dilutes”. The examples below show how difficult it can be to tell the difference between the double dilutes without genetic testing. Some sources will claim that you can tell the difference by eye: that cremellos have more reddish manes, or that smoky creams have darker bodies, or that the eye color differs based on base color, but none of those claims are set in genetics. It may be possible to discern genotype based on parentage.
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The double dilutes can be confused with each other, as well as with champagne (see below) or very advanced grey.
Black + CrCr = smoky cream
Chestnut + CrCr = cremello
Bay + CrCr = perlino
The green eye of cremello Morgan stallion, Amberfield's Desperado.
Blue eyes on Gambler's Midas Touch, a perlino TWH stallion.
The Key, a smoky cream Welsh Pony (Section B) stallion. Confirmed EE/Aa/CrCr.
Hydro's Pawnee Bill GLC, a smoky cream Missouri Foxtrotter stallion.
SFG Infinity and Beyond, a cremello Morgan gelding.
Saphiro, a cremello Lusitano stallion. Confirmed ee/AA/CrCr.
Suyikty, a perlino Akhal Teke filly. Her parents were both buckskins.
DEM Capernicus, a perlino Lusitano stallion.
Champagne
Champagne (Ch) lightens the base color similar to the cream gene, but it is not dose-related (two copies does not increase expression). Champagne horses are born with pink skin around the eyes, muzzle, and genitals that becomes mottled shortly after birth, and may have brown hooves rather than black. They are often born dark, appearing closer to their base color, and lighten as they mature. They also have green-blue eyes at birth that become hazel-amber and an unusually shiny, iridescent coat due to their unique hollow hair shafts, similar to a Weimaraner dog. Heterozygous champagne is indicated by n/Ch since champagne does not have a recessive form.
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The champagne gene is only found in certain breeds with North American heritage, like Tennessee Walking Horses, Missouri Fox Trotters, Quarter horses and related breeds, Miniature horses, Spanish Mustangs, and a few others. Champagne color is so named for TWH mare Champagne Lady Diane, who sparked an interest in the color in many people, though it was later discovered that the gene had existed (and been misidentified) long before Champagne Lady.
Black + Ch = classic champagne
Chestnut + Ch = golden champagne
Bay + Ch = amber champagne
Seal bay + Ch = sable champagne
Unknown champagne foal with pink unmottled skin and blue eyes.
Hazel eye and mottled skin of Sweet Champagne, an amber champagne 7/8 Arabian mare.
Classic champagne appears as a mousy, chocolate-grey color. Shade can vary from horse to horse, as well as on the horse itself; classic champagnes can be unevenly shaded, unlike the other champagnes which are usually a consistent color all over. Classic champagne can be confused with grullo, liver chestnut, or rose grey.
Ms Dowdy Doc Bars, a classic champagne AQHA mare.
Champayne Callie, a classic champagne AQHA mare.
Sjoerd's Wicked Cool, a classic champagne Georgian Grande (Friesian x Saddlebred) stallion. Confirmed EE/aa/nCh.
Gold champagne manifests as a light gold body with a reddish or flaxen mane and tail. It may be confused with palomino or red dun.
SW Champagne Class, a gold champagne AQHA mare, shown as a foal and a yearling. Note the nearly chestnut coloration at birth.
Jil Doccita Gold, a dark gold champagne AQHA mare.
Zippo's Millenium Bug, a flaxen gold champagne AQHA mare. Note the pink-skinned muzzle.
Breed Spotlight: American Cream Draft
Despite their name, the American Cream gets its signature color from the champagne gene, not cream. Most American Creams are gold champagne, just as the breed's foundation mare "Old Granny" likely was. Because the Creams' number had dwindled during the age of agricultural mechanization in the United States, the American Cream Draft Horse Association (ACDHA) allows the registration of mares with dark skin and light manes and tails so that they may bolster the genes of the breed; stallions, however, must have pink skin and cream manes and tails to be registered.
Duke's Colonel, an American Cream stallion. Confirmed Ch/Ch and negative for Cr.
BLC Joker's White Russian, an American Cream Draft stallion. Confirmed ee/AA/Crcr/Chch.
Amber champagne consists of an orange-gold body with chocolate points. It may be confused with dun or buckskin.
Pocos Blue Champagne, an amber champagne solid Paint Horse gelding as a foal and as a yearling.
SW Take Care Too, an amber champagne QH stallion. Note the mottled pink muzzle.
Champagne Ambassador, an amber champagne 15/16 Arabian shown as a colt, weanling, and stallion.
Sable champagne has the same genotype as amber champagne, but is used to describe a champagne with a dark bay, brown, or seal bay base color. Some horses classified as sable have happened to test positive for the short-lived and debunked At seal bay marker. Sable is a visually identifiable as a chocolatey shade in-between amber and classic champagne.
California Champagne, a sable champagne tobiano AQHA stallion shown as a colt, yearling, and stallion.
Cream Champagne
To further confuse things, horses can carry both champagne and cream genes. This results in both phenotypes combining to form a paler-skinned horse with lighter freckling and yellow-green eyes that are often light blue at birth. These horses are so diluted that it can be difficult to tell their base color without testing or parentage.
Black + Ch + Cr = classic cream
Chestnut + Ch + Cr = gold cream/ivory champagne
Bay + Ch + Cr = amber cream
Seal bay + Ch + Cr = sable cream
*remember that sable cream is just an amber cream that has tested positive for At or has a seal brown phenotype
Yellow-green eye and pale mottled skin of Vanilla-N-Ice, a gold cream Missouri Fox Trotter stallion.
Blue baby eye of Hesa Champagne Whiz, a sable cream dun AQHA stallion.
Vanzi Te N Te Glo, a classic cream American Quarter Horse filly.
Double T's Texas Champagne, a classic cream Miniature Horse stallion. Confirmed Ee/aa/Chch/Crcr.
Raffelschampagnewish, a classic cream APHA stallion. Confirmed EE/aa/Crcr/Chch. Note the mottled face and groin area.
Awesome Dandy Gal, a gold cream AQHA mare.
I Love a Mystery, an amber cream Missouri Fox Trotter gelding.
RKM Champagne Blanc de Blanc, a gold cream Miniature Horse colt.
Solo Song ExXodus, an amber cream American Warmblood stallion.
WFR Sugar Cookies, a sable cream AQHA mare.
Classical Rock Candy, a sable cream AQHA mare. Confirmed AtAt/Ee/Chch/Crcr.
Double Cream Champagne
Remember that two cream genes has an additive effect? A double dilute horse can also carry a champagne gene (or two), producing yet another, even more diluted phenotype.
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These horses are very pale, almost white, and can only be produced by crossing a cream champagne with a cream (or another cream champagne). They have very pale blue eyes and light pink non-mottled skin. Because they have almost no pigment in their skin or hair, it can be nearly impossible to tell them apart from each other or from non-champagne double dilutes.
Black + Ch + CrCr = classic double cream or smoky cream champagne
Chestnut + Ch + CrCr = gold double cream or cremello champagne
Bay + Ch + CrCr = amber double cream or perlino champagne
Legacy's Frontier Gold, a gold double cream (cremello champagne) TWH stallion. Note the pale blue eyes and unpigmented skin as an adult.
1man's Apollo, an amber double cream (perlino champagne) Missouri Fox Trotter colt. He was born with unusually dark ear tips that lightened as he grew.
Pearl
The pearl gene (prl) is recessive. For expression, the horse must have two copies of pearl (prlprl) or one copy of pearl + cream. Cream can activate the pearl gene and create a pseudo-double-dilute. Because cream and pearl are located on the same part of the same gene and each horse has only two copies of each gene, a horse cannot have two Cr and a prl (or two prl and a Cr). In the absence of cream, the phenotype of homozygous pearl is similar to champagne; it slightly dilutes the body color and often causes pink mottled skin and blue/amber eyes. One copy of pearl will not affect the horse’s color, but can be passed on to offspring. Pearl is one of the more recently discovered dilution genes and is currently only seen in Quarter Horses and Spanish breeds. Pearl was previously known as “Barlink Factor” in QH, but was found to be the same mutation found in Spanish horses, likely due to the Spanish ancestry of QH.
Black + prlprl = black pearl
Black + prl + Cr = smoky black pearl
Chestnut + prlprl = chestnut pearl
Chestnut +prl + Cr = palomino pearl
Bay + prlprl = bay pearl
Bay + prl + Cr = buckskin pearl
FF Ayacuchana, a black pearl-carrying Peruvian Paso mare, and her smoky black pearl filly, SR Saliente. Her sire is a cremello, so her genotype is Ee/aa/prlCr.
Majodero R, a smoky black pearl Andalusian stallion. Confirmed Ee/aa/nCr/nprl. His dam was a liver chestnut pearl carrier and his sire was a perlino. The Paso foal above will lighten to a color similar to this.
Pearl of Peace EV, a bay double pearl Andalusian stallion.
Guindaleza R, a palomino pearl Andalusian mare. She is the product of a liver chestnut pearl carrying mare and a cremello stallion (Saphiro, shown above). Note how similar she looks to a palomino but with pink skin.
Rey PM, a buckskin pearl Andalusian stallion.
Mushroom
The mushroom gene (mu) dilutes chestnut to a sepia- or taupe-colored body with flaxen or nearly-white mane and tail. This color is only confirmed in UK-bred Shetland ponies and is recessive, so it requires two copies for the mushroom phenotype. It may be confused for the silver gene or cream dilutions, but a mushroom-colored pony will always test positive for chestnut coloring (ee).
Bayhall Magic, a mushroom Shetland pony stallion with his winter coat.
Sidonie, a mushroom Shetland Pony mare.
Halstock Cream Caramel Pie, a mushroom tobiano Shetland Pony stallion.
Halstock Suzette, a tobiano mushroom Shetland pony mare.
Dun
Dun (D) dilutes the main body color (leaving the points dark) and adds “primitive markings”: dorsal stripe, leg barring, cobwebbing (or spiderwebbing) on the forehead, a dark face mask, dark ear bars, and/or shoulder blade striping. Unlike some other dilutions, dun affects both red and black pigment, just not at the points. Duns commonly have frosting, or lighter guard hairs highlighting their manes and tails.
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Dun is present in many breeds, including the Appaloosa, Bashkir Curly, Iberian breeds (rare, except in Sorraias), Icelandic, Mustang, Norwegian Fjord, Paint, Paso Fino, Peruvian Paso, Quarter Horse, and several pony breeds.
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Not all duns have all of the primitive characteristics listed above. Three variants of dun account for the wide range in phenotypes: D (dun dilution + primitive markings), nd1 (non-diluted + variable primitive markings), nd2 (non-diluted + non-primitive). D is dominant over nd1, and nd1 is dominant over nd2. A horse with a dorsal stripe without a dun (D) parent might carry nd1 or may just have sooty countershading. nd1 is an incompletely dominant trait, meaning that two copies will have a more obvious effect than one copy. The most obvious trait of nd1 horses is light inner ear hair and a dorsal stripe that ends at the tail head, instead of continuing into the tail hairs like a true dun. nd1 are also more prone to fading than duns and may have a slightly diluted body color due to their asymmetrically-pigmented hair shafts.
Black + dun = grullo
Black + dun + Cr = smoky black dun = smoky grullo
Chestnut + dun = red dun = apricot dun
Chestnut + dun + Cr = palomino + dun = dunalino
Bay + dun = bay dun = zebra dun
Bay + dun + Cr = buckskin + dun = dunskin
This young Campolina mare dramatically showcases many features of dun: leg barring, shoulder blade barring, dark points, tail frosting, and "cobwebbing" or "spiderwebbing" patterns on the forehead. The classic dorsal stripe is not seen at this angle.
R2 Kooter Cat, a buckskin Morgan gelding with a faint dorsal stripe. His parents are a buckskin and a bay. He may carry nd1, giving him some primitive markings without inheriting D from one of his parents.
Obvious spiderwebbing on the face of a grullo AQHA horse.
M R Magnolia Iron, a black frame overo nd1 APHA filly. Light inner ears like Maggie's are a common hallmark of nd1.
Grulla (pronounced grew-yah) is synonymous with blue dun or mouse dun. Shades vary from blue to slate grey to olive undertones. The points, mane and tail, and face are always black, but may become sun-faded. Some breed associations (including AQHA) call this color "grullo".
A grulla Sorraia. Note the frosty guard hairs.
Kansas City Twister, a grulla AQHA stallion with extreme leg barring. Note the dark tips on the back of his ears, another hallmark of dun factor.
Triple Jet Cee Jay, a champagne grulla AQHA stallion. Note the dorsal stripe, diluted black legs and mane/tail, and pink mottled muzzle.
Mark Me Famous, a grulla AQHA stallion (and grandson of Twister, left). Confirmed EE/aa/DD. Note the leg barring, ear bars, and facial cobwebbing.
Fada, a lobo dun Sorraia Mustang mare. Lobo dun is a very dark shade of grulla caused by sooty shading. Her dorsal stripe is still visible from the back. Click the photo to see Fada's color changes from birth to adulthood.
Reining In Diamonds, a smoky grulla AQHA mare. Confirmed Ee/aa/DD/nCr. Because cream doesn't affect black pigment, her color is phenotypically no different than a regular grulla. Her white markings and blue eyes are due to splash white.
Red dun features an orange or pale brown body with darker red points and no black. Apricot dun can be synonymous with red dun, or can be used to describe a red dun with pale mane and tail. Claybank dun is a pale, clay color and is often used to describe unusually pale red dun Kiger mustangs. Red duns can be confused for chestnuts.
SG Frozen Enterprise, a red dun AQHA stallion. Note the dark shoulder stripe.
Blizzard, an apricot dun Pryor Mustang, sparring with Bakken, a grullo. Note the flaxen mane/tail and dorsal stripe.
Sulphur's Music, a claybank dun Sulphur Springs Mustang mare.
Dunalino has the pale gold base color and cream mane and tail of a palomino, but with primitive markings. Dunalinos can be confused for palominos or sooty palominos.
Major Hearts Desire, a dunalino AQHA stallion.
Kona, a dunalino AQHA filly. Note the leg barring and faint dorsal stripe.
Bay dun ranges from a yellowish tan to a dark brown. Bay dun is very common in wild horses and is sometimes called "zebra dun". Horses registered as just "dun" are often bay dun. A very dark or sooty bay dun may be called "coyote dun". Bay duns may be confused with bays or buckskins.
Donner, the bay dun Kiger Mustang stallion that served as the color inspiration for Dreamworks' "Spirit: Stallion of the Cimarron".
Jackson (left), a coyote dun, and Knight (right), bay dun Pryor Mustang stallions. Note the leg bars on both horses and the ear bars on Jackson.
Dunskin has the light tan body of a buckskin with the primitive markings of a dun. It may be easily confused with buckskin.
Hollywood Dun It, a a dunskin AQHA stallion.
RCK Ragtime Tres Oros, a dunskin Morgan stallion. Note his dark base coat Compared to Hollywood.
Dun can combine with other genes to form interesting and unique phenotypes. Often the primitive markings will become diluted along with the base coat.
Ashwood's Angel, a classic champagne grulla AQHA mare.
My Champagne Dun It, a champagne grulla AQHA mare. Confirmed Ee/aa/Dd/ChCh.
Sierra Hesa Chief, a sable champagne cream dun AQHA colt.
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Rooster On The Rocks, an amber cream dun AQHA stallion. He is also technically roan, but it is nearly impossible to see on the heavily diluted base coat. Confirmed EE/AAt/nCr/nCh/Dd/Rr.
Tuffs Frosted Image, a classic cream dun AQHA stallion. Confirmed EE/aa/nCh/nCr/Dd.
Leg bars and dorsal stripe of Finally's Mr. Amos, a perlino dun Morgan stallion.
Breed Spotlight: Fjord
The Norwegian Fjord horse has existed since before the last ice age and has been selectively bred for over 2,000 years, so it’s no surprise that Fjords are known for their dun coloration and primitive markings. All Fjords have the genotype DD; 90% of Fjords are bay dun in color, while the other 10% are another shade of dun. Fjords are easily recognized by their distinct dark manes and tails bordered by thick stripes of light-colored guard hairs; the manes are traditionally cut short so they stand straight up.
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The rarest of Fjord colors is Hvit (“white”), a blanket term for all double-dilute duns (perlino, cremello, and smoky black dun). This color is inevitable and accepted in Fjords, but it is not favored or intentionally bred for.
Brunblakk (bay dun), the most common color.
Rødblakk (red dun). Note the reddish orange points.
Grå (black dun = grullo = “mouse dun”). Note the warm brown-grey color.
Ulsblakk (“white dun” = buckskin dun = dunskin). Note the lighter forelock and tail.
Gulblakk (“yellow dun” = palomino dun). The dorsal stripe can be very faint and the mane/tail nearly all one color.
Fia, a Hvit (double-dilute) Fjord mare. Note the very pale inner forelock and tail.
Ulsblakk – rødblakk – gulblakk – brunblakk – grå
Note the pale forelock stripe and hazel eyes of a Hvit.
Silver
The silver gene (Z) dilutes black pigment, but does not affect red (chestnut). Silver is also known by the names “silver dapple”, “taffy”, and “chocolate” depending on the region of the world, breed of horse, or shade of silver, but the gene is the same. Silver is often accompanied by dramatic dappling, but not always. The silver gene can affect any black- or bay-based color (i.e., any horse with an E allele). Black manes and tails will be diluted to flaxen or silver-grey and a black horse’s body will become a greyish-chocolate color. The black points on a non-black, non-chestnut horse (bay, buckskin, grullo, etc.) will be diluted to a dark chocolate.
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The silver gene occurs in Rocky Mountain horses and related breeds, Quarter Horses, Mustangs, Miniature Horses, Shetland Ponies (USA), Icelandics, Morgans, Tennessee Walking Horses, and others.
This color can be confused with mushroom in Shetlands or with grulla or champagne in other breeds; a grulla will have a telltale dorsal stripe and a champagne will not have a flaxen mane/tail unless it is very sunburnt.
The silver dilution is associated with Multiple Congenital Ocular Abnormalities Syndrome (MCOA), a group of developmental abnormalities of the eye that can range from mildly affected vision to severe cataracts and deformed eyes. Some breeds, such as Minis, are not as affected by MCOA as other breeds. More severe MCOA is generally found in horses who are homozygous silver (ZZ), therefore the breeding of two silver horses is discouraged.
St Clarins, a chocolate silver Gypsy Vanner stallion. Confirmed EE/nZ.
Silbersee Luxus, a silver black Shetland Pony stallion.
Silver Assured, a silver bay AQHA stallion. Confirmed EE/AA/ZZ.
Villa Vanner's Sinead, a chocolate dapple Gypsy Vanner mare.
KTM Silver Dollar, a silver bay Morgan stallion.
Austin, a homozygous black, silver dapple Gypsy Vanner stallion.
Rainbow, a silver dapple Miniature Horse. His white markings and blue eye are likely caused by the splash white gene.
Bar Z's Great Balls of Fire, a silver bay American Shetland Pony stallion. This pony is often misidentified as having a gulastra plume in photos where his mane is flipped.
Lady Jade, a silver dapple tobiano South Steens Mustang filly.
El Chocolate, a very dark palomino Lusitano stallion that is advertised as silver. Silver is not present in Spanish breeds
Breed Spotlight: Rocky Mountain Horse
The Rocky Mountain Horse is a hardy gaited breed native to Kentucky, and is known for its chocolate coat. While the silver gene is relatively rare in other breeds, it is rather common in the Rocky Mountain Horse and is the preferred color. Despite its name, the RMH was developed in the 1800s in the Appalachian Mountain area from a particularly smooth-gaited and well-tempered silver foundation stallion named Old Tobe. Most RMH today can be traced back to one of Tobe's five sons. A higher percentage of Tobe in the pedigree generally produces a more characteristic RMH. The breed's 4-beat ambling gait makes it ideal for trail rides over rough terrain, but it also performs well in farm work or endurance riding. Despite the youngness of the breed, the Rocky Mountain Horse is gaining popularity due to their flashy coloration and their people-loving personalities.
A herd of Rocky Mountain Horses. Any solid color with minimal white markings is accepted by the registry, but flaxen chocolate (silver) is preferred.
Rockies have a higher incidence of MCOA than most other breeds. This silver dapple Rocky has been diagnosed with the eye disorder.
A silver RMH stallion performing the rack, a smooth gait where one hoof is always on the ground.
Silver can also combine with other genes to create interesting dilutions. Often the body will become lighter with additional dilution genes while the mane and tail remain a golden flaxen color. For example, cream and silver interact in an interesting way to dilute the body color in addition to the mane and tail. Smoky black will become a chocolatey or paper-bag brown and buckskin will become a pale, buff color.
Positively Charmed, a silver smoky black Morgan mare. Confirmed E*/aa/nCr/nZ.
Schnaezer's Silver Lining, a dappled silver grulla Morgan stallion. Note the distinct dorsal stripe.
TMV Taylor Made, a silver buckskin Morgan colt. Confirmed E*/A*/nCr/nZ. The diluted points and mane give him an almost champagne appearance.
True Silver Dun It, a silver grulla AQHA mare. Confirmed Ee/aa/Dd/nZ. Note the obvious leg barring and dark face combined with a golden-chocolate mane and tail.
Ridgehaven's Cocoa, a classic champagne cream silver Miniature Horse stallion.
Choco Dock Jr., a silver sooty buckskin Rocky Mountain Horse stallion.
Classic Thunder (left), a classic champagne silver Miniature Horse stallion; and his sire, MF Mi Little Prince Charming (right), also a classic champagne silver. Note the pink muzzles.
Roan
Roan (Rn) causes white hairs to be intermixed with the base color on the body of the horse, but the legs and face generally remain solid. Roan occurs in many breeds, including the Quarter Horse, Paint, Peruvian Paso, Paso Fino, Welsh pony, Miniature horse, and Belgian. It does not occur in Thoroughbreds or Arabians, although another type of roan has been observed in TB descended from Catch A Bird. If a roan horse’s skin is injured, the hair often grows back solid-colored. These are called “corn marks”. The dark points of a roan horse's legs will often end in a spear or upside-down V shape, instead of a horizontal line like a non-roan.
The exact locus (location on a gene) that encodes roan has not been mapped yet, but enough DNA markers have been found to evaluate if roan is present in Quarter Horses and Paint horses; this is designated as Rn. Evidence from Quarter Horse breeding indicates that it is a dominant trait and that roan homozygosity is not lethal in utero (as previously thought). The gene that Rn is located on (called the KIT gene) is so close to the Extension gene that they are usually inherited together; these are called linked genes. For example, if a Ee stallion's Rn is linked to his E, a foal that inherits E from the sire will also inherit Rn; but if that foal inherits e from the sire, it will not be able to inherit Rn.
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Roan can be confused with grey, but roan is confined to the main body of the horse and grey affects the entire coat. Additionally, roan horses are born with roaning; grey horses fade over time and are never born grey. From a distance, roans and dilutes can appear similar; the roan will have a mix of white and colored hairs when seen up close. It can be difficult to tell if a new foal is roan until their first shed.
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Roaning in appaloosa-spotted horses is called varnish roan and is actually caused by the Leopard complex and is discussed in the Appaloosa section.
Roan can occur in multiple-dilutes (any combination of cream, champagne, dun, silver), but becomes almost impossible to discern without the help of DNA testing.
Flaxen Chestnut or dark palomino + roan = strawberry roan
Chestnut + roan = red roan
Palomino + roan = palomino roan
Black + roan = blue roan
Bay + roan = bay roan
Black + silver + roan = chocolate roan
A close-up of the intermixed white and colored hairs of a roan horse, shown on blue roan Astor (see below).
A buckskin roan Welsh Pony showing the characteristic inverted V shape of the dark points on the legs.
If a brand is not held on the skin very long, the hair may grow back with the base color, like a controlled corn mark, instead of staying bald or growing back white, like on Cosmos, a bay roan AQHA colt.
Nynwood Echo, a palomino roan Welsh Pony (Section A) stallion.
Cloud, a light palomino roan Pryor Mustang stallion.
Kissin The Girls, a red roan AQHA stallion.
Peptoboonsmal, a red roan AQHA stallion.
Blue Moon, a blue roan Nokota stallion. This is a wild horse; all the dark corn marks on his body are likely from sparring with other stallions.
Astor van de Vilert, a blue roan Dutch Draft stallion. Although he doesn't have an all-black mane and tail like most blue roans, the dark points and intermixed white hairs confirm his color.
Plumb Silver Hancock, a silver blue roan ("chocolate roan") AQHA stallion. Confirmed Ee/aa/Rnrn/nZ.
Grace, a silver smoky black roan ("chocolate roan") Rocky Mountain Horse mare.
KN Fabulous Fling, a buckskin roan Quarter Horse filly.
High Rolling Rimrock, a bay roan AQHA stallion. Note the bay points and corn marks.
Morgan Dun In Stone, a perlino champagne dun roan AQHA stallion. This horse is diluted to about as close to white as a horse can get without actually being white. Confirmed Ee/AA/Dd/nCh/CrCr/nRn.
HZ Ima Georgia Peach, a grulla roan AQHA mare. Roan becomes less obvious on already-diluted base colors.
Gypsys's Prescription, a sable roan AQHA mare. Confirmed EE/Aa/nRn.
Rock's Champagne Hope, a classic roan TWH mare.
Grey
Grey (G) causes a progressive, permanent depigmentation of the coat over several years. Grey is one of the strongest modifiers. A horse that carries the grey gene is born one color based on their other color genes and slowly becomes lighter and lighter grey until they are almost white and the original color is no longer visible. Usually the skin color doesn’t change, but dark-skinned horses may become pink around the nose, eyes, or genitals. Most horses go through several phases of beautiful dappled grey before reaching their final coat color of white or fleabitten grey. Homozygotes are more likely to become solid white and grey faster than heterozygotes. Nearly all horses carrying the grey gene will be totally greyed out by age 8-10; most will grey faster.
Fleabitten grey is a white or light grey coat with dark specks that look like “flea bites” all over. The fleabites are areas of repigmentation and may be red, brown, or black and do not always reflect the original base color of the horse. Evidence shows that heterozygotes are more likely to become fleabitten greys than homozygotes.
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Grey is present in almost every breed, but is common in Arabians, Welsh ponies, Quarter Horses, and Percherons. Many Andalusians and nearly all Lipizzaners and Boulonnais are grey. A small number of Thoroughbreds are grey and are all descended from Alcock’s Arabian, a stallion from the 1700s. Because grey is a dominant gene, it can easily take over in a breeding population and can be difficult to breed out. Many breed associations register greying horses only as “grey”, making it difficult to trace coat colors through pedigrees.
Very advanced grey horses are often confused with albino, which has never been reported in horses. True albinos lack the ability to produce any pigment, so they would have very pale eyes and completely pink skin. There are a group of uncommon color mutations collectively called “dominant white” which cause a horse to be born almost completely white, like an all-over pinto pattern, but they will usually have brown eyes, sometimes blue. Lethal White Overo Syndrome will cause a very pale foal with ice-blue eyes that may also be misidentified as albino, but is actually a fatal maximally-expressed pinto pattern. Early stages of grey can often be confused with roan, but a roan will have permanent dark points and a grey will not.
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Because greying is essentially a disease of the melanin-producing cells in the hair follicle, grey horses are predisposed to melanoma, a tumor of the melanocytes. This may also be due to Grey and increased melanoma risk being on the same gene. Up to 80% of grey horses will develop a melanoma in their lifetime, but most are benign (non-cancerous).
1980 Kentucky Derby and Preakness Stakes winner, Spectacular Bid, a bay-gone-grey TB stallion pictured from age 2 ("steel grey") to 25 (fleabitten grey).
Lipizzaner mares and a foal from Vienna’s Spanish Riding School. Note the all-white mare on the left, the mare with some dapple grey on her rump in the middle, and the black foal on the right.
The Spanish Knight, a dapple grey Warlander (Friesian x Andalusian) stallion.
Bellissima - 46, a grey Lipizzan mare.
A team of advanced grey Percherons on Mackinac Island. The horse on the left is solid grey and the horse on the right is fleabitten grey.
Cortesana XXXVI, a grey Andalusian mare.
Comico IV, a bay-going-grey Andalusian stallion. Confirmed Ee/Aa/Gg. This stallion is a bit of a genetic mystery because he is over 20 years old (born 1995) and is still not completely grey. It has been suggested that his single grey gene is somehow being suppressed by an unknown mechanism (perhaps rabicano, discussed below).
Asempaz, a buckskin-going-grey Akhal Teke stallion. This pinky shade of grey is often called "rose grey" and occurs as bay, buckskin, chestnut, etc. go grey.
Nasheetah MVA, a chestnut-going-grey Arabian filly.
A pair of grey Percherons pulling a Grand Hotel carriage on Mackinac Island. Notice the different ways these two horses greyed; the individual on the right may have had a flaxen mane before greying, or it may have greyed faster than the body. The horse on the left likely started life with a black mane.
“Bloody shoulder” markings can occur on any breed of fleabitten grey and do not have to be on the shoulder. These marks are usually reddish (but sometimes brown or black) and are caused by extremely concentrated flea bites. Legend has it that only the most loyal and courageous horses have the bloody shoulder mark bestowed upon them.
Sanaya, a fleabitten grey Arabian mare with bloody shoulder markings.
Tap For Luck, a grey TB mare with bloody shoulder marks.
Jacara, a grey Andalusian mare with a bloody shoulder mark on her hip.
Fullbridled, a grey TB stallion shown in 2011 (left) and 2014 (right), with a bloody shoulder mark across his barrel. The mark is an area of repigmentation.
A foal is never born grey; however, it is sometimes possible to tell from birth if they will become grey. Some grey foals will have a grey muzzle and "goggles" or "eyeglasses" around the eyes. These foals will likely grey very quickly. Another common adage is that very dark foals will grey, but foals born with a light-colored baby camouflage coat will not become grey. Grey is essentially a disease of the pigment cells that causes them to over-produce pigment until they "burn out" and no longer produce pigment, making the horse white. Foals that will grey are often born with hyperpigmented black skin instead of the more common salmon-colored foal skin; it will be easiest to see around their eyes.
A newborn Andalusian filly showing grey goggles.
Silverstone Noble Ash, a black-going-grey Morgan filly.
WB Munchakin, a buckskin-going-grey Welsh/Arabian/Miniature colt.
Cava, a APHA filly born a light, psuedo-buckskin, who is shedding out to a much darker color. Neither of her parents are grey, so she will not grey.
Atina, a pitch-black newborn Lipizzan filly who will grey like both of her parents.
Rabicano
Rabicano is characterized by a skunk or coon tail, a tail with white outer hairs and base-color inner hairs. Some rabicanos also have roaning limited to the barrel or stifle (area in front of the hip), often arranged in striations along the ribs. Rabicano can occur over any body color and is present in many breeds, even breeds that do not carry true roan, such as Arabians. Rabicanos can be confused with early greying or with true roans, but look for the skunk tail and localized roaning to tell them apart.
High Brow Cat, a chestnut rabicano AQHA stallion and all-time leading cutting horse sire.
The skunk tail of Skunktail, a bay rabicano "sabino" TB gelding.
Copy Cat, a genetic clone of High Brow Cat. Although they express their identical genes differently (note the different facial and leg markings), they both express rabicano.
Nynwood Philosopher, a bay rabicano Welsh Pony colt.
Tangys Stinky Doc, a bay rabicano Paint gelding. His sale ad lists him as a roan, but he is quintessentially a rabicano due to the presence of a skunk tail and white ticking along the barrel and on the stifle.
Aswad Shahwan BWA, a black rabicano Egyptian Arabian stallion.
Rock Ranch Sonadora, a black rabicano Gypsy Vanner mare.
Fronbach Destination, a bay rabicano Welsh Pony stallion.
Fronbach Destination, a bay rabicano Welsh Pony stallion.
Polka Dot Levis, a chestnut minimal rabicano AQHA mare. She has little to no flank ticking, but a very obvious coon tail.
Gulastra Plume
Gulastra plume is a grey, silver, or even flaxen-looking tail on an otherwise non-grey, non-silver, non-flaxen horse. The mane will be almost completely dark. Gulastra plume can occur on any base color and the tail generally darkens with age but never completely disappears. Bay horses with gulastra plume are usually "wild bay" with relatively little black on the body. It is not known what causes gulastra plume, but it may be a form of color-shifting. It was once theorized that it was caused by some sort of skewed "sabino".
It is so named for the Arabian stallion Gulastra, who was himself a plain chestnut, but sired many plumed horses. This trait is most common in Arabians and Thoroughbreds.
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Do not confuse gulastra plume with "foal flaxen", which is a light-colored tail that can take several years to fully shed out. Rabicano looks similar to gulastra plume, but will usually have visible white ticking on the barrel or stifle and the tail is usually only bordered by white.
Arabian Kissed, a wild bay TB filly with probable foal flaxen.
Helyna's Dreaming, a wild bay TB filly with gulastra plume or foal flaxen that is slow to shed.
Reflection Stone, a black Arabian stallion with gulastra plume. Confirmed black, non-grey.
Unraveled, a bay Morgan mare with presumed gulastra plume. Other horses in her pedigree have had silver-tinged manes and tails or flashy white markings.
Starfire Knight Hawk, a bay Gypsy Vanner, as a colt (left) and 2-year-old (right). His blonde tail is likely leftover foal flaxen since it and his mane have darkened to near-black by age 2.
Intro to Pintos
Pinto is a coat color generally characterized by flashy, asymmetrical white markings. “Paint” is a breed of horse descended from Quarter Horses or Thoroughbreds with pinto markings. White markings will have pink skin underneath the hair, although the margins of the markings may have dark skin. Pinto markings can occur over any base color, including dilutes, roan, and grey. Not all breeds have pinto genes or allow them in their registries.
Generally, a pinto marking includes any white patches on the body, as well as any white marking on the face extending past the eye or lip, or any leg marking extending past the knees/hocks (though there are always exceptions).
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Piebald is an old British term describing a black and white pinto; skewbald describes pinto markings on any color but black. Neither term is specific to any particular pattern.
Generally, any white markings extending past the black legs and face in this picture will be considered a pinto marking.
Tobiano
Tobiano (TO) causes white markings that cross the back. Tobiano is often characterized by vertical white markings that are ovalish in shape, white legs, brown eyes, and face markings similar to that of a solid horse. Two-color tails are good indicators of tobiano, as they are rare in non-tobianos. Blue eyes are uncommon in horses that do not carry other pinto genes. Heterozygous and homozygous tobianos are visually indistinguishable, although cat tracks (or ink spots) across the whites are often indicative of homozygous tobiano.
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The tobiano locus is located so close to the KIT gene that it is considered impossible for a horse to carry tobiano plus any more than one other KIT mutation (ex: roan, SB-1, and dominant white). This means, for example, that a roan tobiano horse cannot be homozygous for either trait
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A maximally-expressed tobiano pattern is sometimes called a Moroccan pattern (though the pattern has nothing to do with Morocco). These horses will be nearly white with a dark head and possibly a small colored belly spot and bi-colored tail. A minimally-expressed tobiano will be nearly solid, usually with multiple white legs and small white markings near the shoulder or rump.
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Sometimes palomino or buckskin tobianos will have unusual darker patches within their colored spots; this is called calico and is presumed to be due to an interaction between cream and tobiano, causing some areas of the body to be non-diluted.
John Simon, a bay tobiano Paint Horse stallion. Note the whites crossing the back, white legs, ovalish markings, bi-colored tail, and brown eyes.
General Hector, a black tobiano TWH stallion. Note the dark head, bi-colored tail, and white legs. Confirmed EE/aa/TOTO.
Martha, a buckskin minimal tobiano Chincoteague Pony mare.
Fifteen Friends of of Freckles, a bay tobiano Chincoteague Pony mare with cat tracks.
Paint Em All Dun, a grullo tobiano APHA colt. Confirmed Ee/aa/DD/TOTO, negative for overo.
Chocolate Dip, a bay Moroccan (maximum tobiano) Chincoteague Pony mare.
Tres Colores de Ciente, a buckskin calico tobiano Paso Fino gelding. Note the non-diluted patches on his hip, wither, and barrel.
EMH Paints Dru Inyan, a grullo tobiano APHA stallion with ink spots on his neck, Belton spots on his face. The spots around his coronet bands are ermine spots, and the spots on his legs are distal spots.
Canterbury All That Jazz, a black homozygous tobiano Miniature Horse stallion with cat tracks.
Misty III, a palomino tobiano Chicoteague Pony mare.
Maisie, a blue roan tobiano Cob mare. Her genotype must be E_/aa/nRn/nTO.
Frame Overo
Frame overo (O or Fr) causes white markings that spread from the sides of the belly outwards and do not cross the back. Frame overo is often characterized by horizontal markings, jagged margins, top-heavy white face markings, and dark lower legs and tail. Blue eyes only occur if they are covered by a white marking. Frame on its own may manifest as a nearly-solid horse with only limited white markings; frame can be boosted by another pinto pattern to increase the amount of white. A maximally expressed frame overo will never appear completely white. The body's white markings are usually “framed” by color when the horse is viewed from the side, hence the pattern's name.
In North America, "overo" can be used to describe anything that is non-tobiano, which can be confusing. Using the term "frame" or "frame overo" clarifies that you are talking about the pattern caused by the O (or Fr) allele. In South America, "overo" means any white-patterned horse.
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Frame overo is a dominant gene. A foal born with two frame overo alleles will have Lethal White Overo Syndrome (LWOS; also abbreviated OWLS, LWS, OLWS, or OLWFS); it will be born nearly completely white with ice-blue eyes and light pink skin. The nerves in the digestive system do not develop fully as a side effect of the overo mutations, and the bowel cannot function. Foals will suffer and die within 72 hours if not humanely euthanized. Heterozygous overos (nO or Frfr) do not express characteristics of LWOS. A nO x nO cross has a 25% chance of producing a OO (lethal white) foal. It is not possible for a true frame overo horse to not carry the LWO gene; they are one and the same. Because some minimal frame overo horses can appear to be non-pinto horses, populations containing overo should be DNA-tested before breeding to avoid LWOS.
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Frame overo is most commonly seen in North America and (rarely) in South America, in breeds derived from Spanish horses.
God's Glorious Sky, a buckskin minimal frame overo Morgan mare.
Sky Walker AB, a palomino frame overo Morgan mare and dam of God's Glorious Sky (above).
GFR Barlnk Dun Kiden, a red dun maximum frame overo AQHA/APHA stallion. Note the "frame" of color around his back and down his rump.
Flower, a grey probable-frame overo Australian stock horse gelding whose pinto pattern is only visible when his hair is wet. He began life as a darker color and as he greyed, his hair turned white but his skin stayed black. An outdated term for a grey (white) pinto is a "ghost pinto".
Hot Scotch's Legacy, a black maximum frame overo APHA colt.
Single Tall Mocha, a chestnut minimal frame overo APHA mare. This horse could easily be mistaken for a solid (non-patterned) horse and shows why it is important to test at least one parent for frame overo before breeding.
Justa Cool Secret, a chestnut rabicano minimal frame overo APHA mare. She has only a small belly spot to give away her pinto genes.
Hes Stylin, a bay frame overo APHA stallion with extensive dark skin spots, or Belton spotting, on his face. His patterning mimics tobiano, but he is frame overo based on his parentage. Belton spots appear to be linked to frame overo.
M R Magnolia Iron, a black frame overo nd1 APHA/AQHA filly. The only hint to her nO status is her partial blue eye.
Barlink Sally Jo, a solid chestnut frame overo AQHA/APHA mare. Note the top-heavy wide blaze hinting to her frame status.
Splash
Splash white (SW) causes pinto markings that originate on the bottom of the horse and spread upwards, like the horse ran through some white paint and splashed it on their legs, belly, and face. Splash is often characterized by crisp margins on the white markings, bottom-heavy wide blazes, tall socks, belly spots, and blue eyes (even if the white doesn’t touch the eyes). A seemingly non-pinto horse with blue eyes and 4 socks is likely caused by splash. Some splash horses are deaf due to lack of pigmentation in the hairs of the inner ear.
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Splash white mutations are dominant and additive; combinations of splash or splash + another pinto pattern can cause extensive white markings. The Splashed White Project has lots of examples of DNA-confirmed splash and splash-combination horses.
Four mutations of splash have been identified:
SW1: Present in the Quarter Horse, Paint, Morgan Horse, Trakehner, Miniature Horse, Shetland Pony and Icelandic Horse. Homozygous SW1 is non-lethal.
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SW2: Present only in certain lines of Quarter Horse and Paint Horse (suspected to originate in the QH mare, Katie Gun; propagated by her son, Colonel's Smoking Gun). Considered homozygous non-lethal based on a single horse. May be deaf.
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SW3: Rare. Present only in certain lines of Quarter Horse and Paint Horse (suspected to originate with AQHA/APHA stallion, TD Kid). May be deaf. May be homozygous lethal; avoid SW3 x SW3 crosses.
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SW4: Rare. Only identified in the I'za Last Jet line of Appaloosas. May cause splashed white or a broad blaze.
SW1 and SW3 are both located on the MITF gene, meaning a horse can have a maximum of two copies of SW1 and/or SW3. SW1 is an incomplete dominant; a single copy causes leg and face white, while two copies will cause white extending up onto the body. SW1/SW3 horses will be nearly or completely white. Lack of a confirmed living SW3/SW3 horse suggests that homozygous SW3 is embryonic lethal.
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SW2 and SW4 are on the PAX3 gene. SW1 can boost SW2 to create a horse with more white. SW1/SW1/SW2 horses will be nearly or completely white.
Maestro, a chestnut splash Salt Wells Creek Mustang gelding.
Gunners Nu Chex, a smoky black splash AQHA/APHA mare. Confirmed EE/aa/nCr/SW1.
Colonel's Smoking Gun (left), a chestnut splash AQHA/APHA stallion, and Dun Gotta Gun (right), a bay dun splash AQHA stallion. Both horses carry SW2 from their dam, Katie Gun. Colonel's Smoking Gun was deaf.
I Might Be A Redneck, a chestnut splash AQHA/APHA stallion. Confirmed SW1/SW1, frame negative, pearl carrier.
Diamonds For A Win, a sorrel splash + frame overo AQHA/APHA mare. Confirmed ee/Aa/nO/SW1.
Fergies Kitty Hawk, a silver bay homozygous SW1 Miniature Horse mare. Confirmed E*/A*/SW1SW1/Z*, negative for O.
Silky Keno, champion black splash frame overo APHA mare, shown with her colt, Echo In The Night. She has two blue eyes.
Tovero
Tovero (sometimes called tobero) is a somewhat outdated term used mostly by breed registries and describes a phenotype, not a specific genotype. Several pinto patterns can combine to form a pattern which can be characterized by a Medicine Hat (a dark bonnet over the ear area), dark spots around the mouth, and/or islands of dark color surrounded by white (“shield” markings) on the chest, flanks, and base of the tail. One or both eyes will usually be blue. Tobiano is epistatic with frame overo, meaning it can mask frame with whites that cross the back and are more vertical in nature.
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Any horse matching this phenotype can be called a tovero, but it is most accurate to instead use the names of the individual patterns the horse carries (ex: splash + tobiano).
Johnny Carson, a sorrel Medicine Hat APHA gelding. Although he does not carry frame overo (he is tobiano + sabino-1 or W20), he has a tovero phenotype. He has one blue eye.
Shaman, a bay Medicine Hat (tovero) South Steens Mustang stallion. Though he lacks the mouth spots, he has two blue eyes and dark chest and flank shields.
Pacific Mad Hatter, a black tovero + splash Miniature Horse stallion. Confirmed nO/TO*/SW1.
Coconut, a bay tovero Medicine Hat Quarter Horse filly. Note the shields of color on the chest and stifle, dark spots near the mouth, and two blue eyes.
Call Me Billy, a black SW1 + tobiano APHA stallion.
Sabino & Dominant White
Sabino is visually characterized by white markings starting from the belly up with jagged, lacy edges or roaning. Sabino often manifests as belly spots, extended “apron” face markings, and lacy white socks ending above the hocks with pointy margins. Sabino only causes blue eyes where white touches them.
The first sabino mutation discovered was a dominant gene called SB1. Two copies of SB1 causes a horse that is at least 90% white, called sabino-white. SB1 can cause totally white horses, but does not cause Lethal White like frame. It can combine with other pinto patterns to add a roany or lacy appearance. SB1 is found in the Tennessee Walking Horse, Paint Horse, Miniature Horse, Azteca, Missouri Foxtrotter, Shetland Pony, Spanish Mustang, and Pony of the Americas.
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“Sabino” is often used to describe the sabino phenotype, and not necessarily a horse with the SB1 gene. Not all "sabino" horses carry SB1. Clydesdales, for example, are well known for their extensive lacy white feathered legs, white face markings, and white belly patches, but do not carry SB1. Further research is needed to understand what causes sabino in other breeds, but some sabino-like patterns that are not SB1 can be explained by the dominant white patterns. The dominant white alleles and SB1 affect the same gene and produce a similar range of phenotypes, but since SB1 was mapped first, it does not follow the same nomenclature as the other W mutations; because of this, any additional mutations on this gene are likely to be named with W instead of with SB. A single horse can only have two sabino or W mutations, or sabino/W and roan, or sabino/W and tobiano, since they are all located on the KIT gene. It is not uncommon for horses with W mutations to be colloquially called "sabino".
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Some patterns, such as sabino-like whites and appaloosa, can cause a phenomenon called "color shifting", where the distribution of color on the horse can be skewed, causing blacks to become a pewter color, bays to become bronze, or manes/tails to become almost flaxen.
Magic Mans Color Prints, a bay maximum frame overo + SB1 sabino Miniature Horse stallion. Confirmed EE/A*/nO/SB1, negative for silver and splash. The light mane and tail are likely color-shifted.
Pusher's Coat of Colors, a black SB1 sabino TWH stallion. Note the jagged white markings extending up from his rear sock and the roaned margins, especially on the barrel and front legs.
Pacific Petite Sirah, a bay SB1 sabino Miniature Horse mare. The sabino white ticking gives her a pseudo-roan appearance and her mane is likely color-shifted, causing it to be reddish rather than black. Confirmed EE/AA/SB1, negative for O.
Anchor, a maximum white Marwari stallion. He is likely SB1/SB1. This color of horse is called a nukra in India and should not be misidentified as albino.
SBH Phoenix, a bay SB1-negative sabino Clydesdale stallion. Note the lacy belly patches and socks, as well as the wide blaze extending onto the chin. His mane is nearly flaxen, likely due to color shifting from his untestable white pattern.
Nostalgias Dirty Money, a black sabino + splash Miniature Horse stallion. Confirmed EE/aa/SB1/SW1, negative for O.
Patches, a flaxen chestnut badger-faced Paint mare, likely splash + a sabino-like pattern. Note the extensive face marking and blue eyes (due to splash) plus the roany margins from "sabino". Badger face is not linked to a specific gene, but is possibly due to an occlusion over the white marking.
Dominant white (or white spotting) is a blanket term for a group of more than 20 gene mutations (W) that cause varying amounts of pigment-free skin, ranging from almost non-pinto, to obviously pinto, to completely white. "Dominant" should be thought of in terms of the dominant nature of the gene, not that the horse will (necessarily) be predominantly white. These mutations cause pink skin and brown eyes.
Dominant white mutations may combine with each other or with other pinto patterns to create an even wider array of white markings. Some dominant white mutations are lethal in a double dose, such as W5 and W10. Most mutations are limited to specific lines within breeds. A list of all identified dominant white mutations and their suspected founders can be found here.
W20 is an older mutation found in many breeds. A single copy acts as a booster, causing extended socks and blazes on "solid" horses or producing an additive effect with other W or non-W patterns, while two copies causes a "sabino" phenotype. W20 is commonly seen in combination with other W or pinto patterns.
Jango, a black W20/W20 Gypsy Cob stallion. Note the sabino-like white patterning.
JJP Grace Undenied, a sorrel maximum-white SB1/W20 APHA mare, and her bay Medicine Hat colt, Johnny Carson. The colt has inherited tobiano from his sire and either SB1 or W20 from his dam, which is boosting the tobiano and causing the roany borders.
Make Me Shine, a liver chestnut n/W20 APHA stallion. Notice his tall socks and wide blaze that are rather subtle for a Paint horse, but a little more flashy than a solid horse's markings.
W22 is a unique mutation that essentially occurred right next to a W20 mutation, meaning that W22 is actually W20 + W22 on the same KIT gene; the two mutations cannot be separated when passed onto offspring. However, a horse can carry W22 on one KIT allele and W20 on the other, causing an all-white phenotype. Unfortunately, some genetic labs have reported a positive result for a single W22 gene as W22/W20, and a positive result for a W22 and W20 as W22/W20/W20 (implying the horse has 3 KIT genes), leading to much confusion. W22 originated in the TB mare Not Quite White, who also carried W20, and was propagated by her son, Airdrie Apache.
Airdrie Apache, a chestnut W22 TB stallion (son of Not Quite White).
Arctic, a W22/W20 TB stallion. Although his hair is all white, he has some dark speckled skin.
W5 is found in Thoroughbreds descended from Puchilingui. It causes tall, irregular socks and large face markings.
Puchilingui, a bay TB stallion and origin of the W5 mutation.
Sato, W5 son of Puchilingui, and the first palomino pinto TB in the world.
W15 is found in Arabians and is suspected to originate from Khartoon Khlassic, although the white expression is more obvious in his descendants. W15 horses appear "sabino", may have blue eyes, and often have white legs and white over the cheeks, throatlatch, and neck.
Rhevelation, a bay W15 Arabian stallion, grandson of Khartoon Khlassic.
Khartoon Khlassic, a bay purebred Arabian stallion and suspected source of W15.
Pikhasso, a bay W15 Arabian stallion, son of Khartoon Khlassic.
W10 was the first dominant white mutation discovered in Quarter Horses and is found in descendants of GQ Santana. White hairs increase and dark hairs decrease as the horse ages.
GQ Santana, a APHA stallion and originator of the W10 mutation. Note the dark skin pattern under the white hair.
W4 (aka CW) is the mutation responsible for the all-white coloring of the Camarillo White Horse. The mutation originated in Camarillo foundation stallion, Sultan. Any horse carrying W4 is eligible to be registered as a Camarillo White.
Sultan, the foundation CWH stallion and originator of W4, with Adolfo Camarillo.
El Patron, a CWH stallion, with Harold Parker, who is credited with reviving the breed.
W14 is a mutation found in Thoroughbreds, suspected to originate from Shirayukihime ("snow white"), a totally white Japanese racehorse sired by Sunday Silence (USA). Almost all W14 horses are completely white.
White Vessel, a W14 TB stallion out of Shirayukihime. Note his partial blue eye.
Buchiko ("spotted girl"), a bay W14 TB filly out of Shirayukihime.
Marble Cake, a chestnut W14 TB mare out of Shirayukihime.
W21 is found in Icelandic horses and originated from Ellert frá Baldurshaga. It causes a splattering effect called “ýruskjóttur” (“speckle”).
Ellert frá Baldurshaga, a bay dun W21 ýruskjóttur Icelandic stallion.
Intro to Appaloosa
Appaloosa patterning is characterized by varying degrees of white on the body with Dalmatian-like spots. Besides the Appaloosa, this patterning is also present in breeds such as the Knabstrupper, Pony of the Americas, British Spotted Pony, Noriker, Sugarbush Spotted Draft, and less commonly in the Miniature Horse and Mustang. Because these patterns are found in breeds other than the Appaloosa, a lowercase "a" is often used to mean Appaloosa-spotted horses that are not Appaloosas. Spotting can occur with any any base color, any dilution/modifier (champagne, dun, roan, etc.), and even pinto, though it can be difficult to come across such combinations without crossing different breeds.
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The genetics of appaloosa spots are still being researched, but the current understanding is that they are controlled by two different genes: Leopard Complex (Lp) controls the level of spotting and Pattern-1 (PATN1) controls the extent of white. There are definitely other white pattern genes that also play a role, but only PATN1 is testable at this time. PATN1 is inherited as a dominant trait, while Lp is inherited as an incompletely dominant trait, meaning that LpLp homozygotes have a different phenotype than Lplp heterozygotes.
PATN1/PATN1
PATN1/N
N/N
In the presence of Lp:
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PATN1/PATN1 will be ~80-100% white.
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PATN1/N will have a medium-large blanket.
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N/N will have a small blanket.
lplp horses do not show spotting, even if they have inherited PATN1. These are called "non-characteristic" appaloosas.
Lplp horses will have spotting over the whites.​
LpLp horses will have zero or very few spots.
In addition to the obvious spotting, the leopard complex also causes other characteristics that are representative of the Appaloosa and related breeds: mottled skin near the muzzle, eyes, and anus; striped hooves; and visible white sclera around the iris, like a human's. These characteristics are not exclusive to spotted breeds, but should always be present in a horse with Lp. The leopard complex is also associated with a sparse mane and tail, sometimes called a rat tail; this is genetic and not related to the health or care of the horse. Some spotted horses will have irregular white markings on the legs that do not touch the hooves, called lightning marks.
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Lp also causes some level of progressive roaning over time, called varnish roan. Varnish is not a true roan and is not greying (although a horse can have both). Hair over the bony prominences, like hips and the face, often remains dark, called "varnish spots". Some horses will become nearly white and some horses will hardly varnish at all over their entire lifetime.
Visible eye whites (A), striped hooves (B), mottled genitalia (C), mottled muzzle (D), and varnishing (E) associated with the leopard complex.
The mottled face of Ima Cool Kelo.
Note the obvious eye whites of Tattoo (Shining Royse).
Chacos, a blue roan + varnish roan Appaloosa x Hanoverian gelding.
Homozygous leopard complex (LpLp) is also associated with Congenital Stationary Night Blindness (CSNB), an inherited, non-progressive disease of the retina that causes markedly decreased vision in low light; heterozygous horses are not affected. Appaloosas are also more prone to equine recurrent uveitis, also known as "moon blindness", an acute inflammation of the eye that flares and can cause blindness if untreated, but it has not been found to be linked to the leopard complex.
Endo, a varnish Appaloosa gelding. He began life as a bay snowcap (top left) and quickly began varnishing, even as a yearling (top right). He suffered from such severe recurrent equine uveitis that both eyes had to be removed, but it doesn't slow him down. He is now mostly white with bay remaining on his snout, ears, and bony parts of his legs. Read more about Endo's story here.
Blanket Patterns
Blanket patterns present as a white blanket with dark spots over the hips that can even spread over the back. They are caused by heterozygous leopard complex (Lplp) and either one or no copies of PATN1 -- one copy generally causes a larger blanket and no copies usually results a very minimal blanket, perhaps due to other unknown pattern genes.
Wranglers Royal Miss, a black blanket Appaloosa filly.
Master In Command, a chestnut blanket Appaloosa stallion.
Tonks Tiger Lily, a grulla minimal blanket Appaloosa mare. Note the darker spots even where there is no blanket.
Sartor's Simply The Best, a bay blanket Knabbstrupper x Warmblood mare.
Snowcap Patterns
Snowcap patterns present as a white blanket with no (or very few) spots over the hips that can even spread over the back. They are caused by homozygous leopard complex (LpLp) and either one or no copies of PATN1 -- one copy generally causes a larger blanket and no copies usually results a very minimal blanket, perhaps due to other unknown pattern genes.
Wranglers Black Magic, a bay minimal snowcap Appaloosa filly.
Honkytonk Wrangler, a black snowcap Appaloosa stallion. Confirmed LpLp.
Ima Cool Kelo, a chestnut snowcap Appaloosa stallion.
Sheza Good Sport, a buckskin minimal snowcap Appaloosa mare and dam of six National or World Champions.
Few Spot Patterns
Few spot patterns present as very few colored spots over a white or nearly-white base coat. They are caused by homozygous leopard complex (LpLp) and usually two copies of PATN1. A nearly-few spot horse may have a very large blanket that covers everything but the head, neck, and lower legs.
Solar Abba Gold, a black few spot Appaloosa mare.
Turkus, a black near-few spot Polish Anglo-Arab gelding. Note the lightning marks on his legs. Lp-induced color-shifting is causing his black to be more of a pewter.
A black few spot Noriker stallion from the Elmar line (the sire line of Norikers that carry leopard).
Looking Glass Faberge, a chestnut few spot Falabella mare.
Leopard Patterns
Leopard patterns present as many colored spots over a white or nearly-white base coat. They are caused by heterozygous leopard complex (Lplp) and usually two copies of PATN1. A nearly-leopard horse may have a very large blanket that covers everything but the head, neck, and lower legs.
Sartor's Showtime, a black leopard Knabstrupper stallion with lightning marks.
Figaro af Hallundbaek, a black leopard Knabstrupper stallion.
Shining Royse, a bay leopard Appaloosa gelding. The light halos around his spots are sometimes called "peacock spots" or "moldy spots".
A black leopard Noriker gelding. This pattern is called "tiger" in the Noriker breed, reflecting a linguistic similarity to "leopard".
Zen, an Appaloosa gelding whose spots are only visible when his hair is wet. He could be a leopard-gone-grey, or possibly an extreme few spot with mottled skin, but no pigmented hair spots.
EZ To Spot, a black leopard Pony of the Americas gelding.
Mighty Incandescent, a grulla suppressed leopard Sportaloosa filly. Her white pattern has been shrunk to cover less of the body, but not enough to be considered a blanket. It is not known what causes the suppression.
Snowflake & Frost Patterns
As its name implies, the snowflake pattern causes small white flecks over the body of the horse that mimic snowflakes. The spots generally increase in number with age. It's not known what causes the snowflake pattern; it may be a form of varnish roan. Snowflake patterns may be confused with the non-appaloosa trait called birdcatcher spots, which are small white spots or ticking that appear on the horse later in life.
Frost appears as a sort of roaning over the back and barrel and may be confused with roan or grey.
Kayitah of Nocona, a flaxen chestnut snowflake Appaloosa mare.
Cayuse Scratch Me First, a grulla frost Appaloosa mare. Confirmed Lplp.
Man O Love, a bay blanket + snowflake Appaloosa stallion.
Willspynow, a bay TB mare with birdcatcher spots and no appaloosa traits. Note the differences from the snowflake pattern.
Monster Magnet, a chestnut snowflake Appaloosa stallion that started life as a snowcap.
Full Of Promises, a bay frost Appaloosa x TB mare.
Non-Characteristic Patterns
Horses that have spotted parents and have inherited a pattern gene (like PATN1), but not the leopard complex (meaning they are homozygous lplp), will be solid colored, but can still produce spotted offspring if bred to a horse with Lp. They do not have mottled skin and may not have striped hooves or eye whites. They are still eligible for breed registries.
Turbo Tonk, a non-patterned chestnut Appaloosa gelding (lplp), and his parents, Sunbeach Honkytonk (top left) and Sirtenly Sirprized (top right).
After Twilight, a non-patterned bay Appaloosa mare (lplp), and her parents, Sunbeach Honkytonk (top left) and Enchanted Ice (top right).
Pintaloosa
Pinto and appaloosa-patterned horses can be bred together to create a unique mixed pattern called pintaloosa. These horses may have a spotted blanket over the hips that blends into a pinto pattern on the front half, or they may appear to be leopard-spotted with white pinto markings "painted" over the spots.
SLR A Twisted Dandy Special, a blue roan tobiano pintaloosa Quarter Pony stallion.
Moosetracks, a bay tobiano pintaloosa Appaloosa x Draft gelding.
Manchado
Manchado is a rare and unique white pattern that has only been observed in Argentina in certain breeds, such as the Criollo, Thoroughbred, Hackney, Polo Pony, and Arabian.
Manchado overo is a crisply-defined, asymmetrical pattern with a phenotype in between a pinto and an appaloosa; individuals may have minimal or significant areas of white containing small splotches and larger islands of color. It is difficult to generalize a pattern that is so unusual, but manchados often have dark legs and a dark head (both with average white markings) and some amount of white involving the mane. Manchado is not testable due to its rarity and is not predictably heritable.
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Most experts agree that the pattern must have some environmental influence since it has only cropped up in one country and in breeds that are not commonly crossed. Some have also theorized that manchado is caused by a rare fungal infection, but the patterning doesn't behave like an active infection (i.e., spreading over time) or like a treated infection (i.e., fading white spots).
Trabag, a well-known chestnut manchado Arabian mare, born in 1946 in Argentina. Note the dark head, dark legs, white mane, crisp margins, and asymmetrical spotted pattern.
Royal Manchado, an Argentinean chestnut manchado TB stallion.
A bay Argentinean manchado Polo Pony.
A bay (likely) manchado Criollo mare.
Chimeras
A chimera is formed when a pair of fraternal twins fuse in the womb and become a single horse with two individual types of DNA. Twins in horses are very rare, and chimeras are very, very rare (only a handful of confirmed chimeras are known across the world). The first clue to a chimera is often a very bizarre coat color, due to the patchwork of two phenotypically different horses merging together. A DNA test will reveal two different results depending on which part of the body is sampled; the two zygotes can be different colors, different patterns, or even different sexes. The most well-known chimeras are brindles.
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The offspring of chimera parents will only inherit one set of DNA from each parent, and thus cannot inherit the flashy chimera coat (although it is theoretically possible, but practically improbable, that the offspring could be also end up being a chimera).
Litningur frá Möðrufelli, a chimeric Icelandic stallion (flaxen chestnut tobiano + black tobiano).
Mosaics (Somatic Mutations)
Somatic mutations are anomalies in the DNA that occur after conception and cannot be passed on to offspring. These alterations can cause cancer or diseases, or sometimes just interesting phenotypes. In horses, somatic mutations are often due to genes being inexplicably “switched on” or “switched off” on certain parts of the body. Somatic mutations are well-studied in dogs.
The horse may appear to be a "frankenstein" of different horses like a chimera, but all of the cells will have the same DNA (unlike a chimera which will have 2 different DNA lines). Another name for an individual with a somatic mutation is a mosaic. Bloody shoulder markings on fleabitten grey horses are not somatic mutations, but solid "mismarks" on appaloosas or roany patches on a non-roan usually are.
Remarkable (aka Lorando B), a bay Swedish Warmblood gelding with the grey gene only “switched on” on his front left leg and chest.
Perfectly Gray, a chestnut-going-fleabitten-grey TB filly with a "blood mark" on her face that would more correctly be called a somatic mutation since it is an area that has failed to grey, rather than an area of fleabitten repigmentation.
Holme Park Van Gogh, a bay Trakhener colt with a patch of black on his neck where the Agouti appears to be “turned off”.
Shimmering Moment, a chestnut TB mare with a white stripe in her tail, likely a somatic mutation or old injury. Her sire is Afleet Alex.
Hang N The Streaker, a smoky black Morgan stallion with a roany leg.
Stetsons Mr Blue, a chestnut + black overo APHA stallion. He is posted all over the internet as a chimera, but he is more likely to be a mosaic caused by "silencing" of Extension (ee).
Brindle
Brindle is a common color in dogs and cattle, but very rare in horses, that gives the appearance of alternating light and dark vertical stripes in the coat along the lines of Blaschko. There is no single predictable, heritable form of brindle, but rather several different phenomena that can produce a brindled phenotype.
One gene mutation has been identified so far that causes inheritable brindle, a hair texture pattern called BR1. BR1 is a semi-dominant X-linked gene, meaning that it is encoded on the X sex chromosome; females have two X and males have one X and one Y. The BR1 phenotype is variable; one copy of BR1 in female horses usually causes a stripe-textured coat, while two copies may cause a sparse mane and tail, but no visible stripes. One copy of BR1 in male horses usually causes a sparse mane and tail, but no stripes, similar to a homozygous female.
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The BR1 pattern can be subtle; the hairs in the stripes are unrulier and less straight than the rest of the coat. The brindled appearance varies with the season and the winter coat may appear “moth-eaten”.
The BR1 study was conducted on the Ima Star Moon Bar line of Quarter Horses and the mutation is testable.
Various phenotypes of BR1 mares. (A) brindle on solid base coat, (B) brindle on bay overo base coat, (C) subtle brindle striping on a mare before and after (D) clipping.
The winter (A) and summer (B) coats of the same BR1 mare. (C) a BR1 stallion with no visible patterning and sparse mane and tail.
Incontinentia Pigmenti is an X-linked genetic disease that can produce a brindle-like phenotype. The stripes come from a combination of light and dark streaked hair from birth as well as the development of itchy or painful skin lesions that can scar and develop into areas of alopecia (hairlessness) or warts, or can grow back as wooly patches. IP also causes abnormalities of the teeth, hooves, and eyes and appears to be fatal to male fetuses. Horses with IP should not be bred.
A mare with incontinentia pigmenti, possibly an offspring of Brenda BattyAtty.
A close-up of the hairless scars along her rump and barrel.
A brindle pattern can also result from a chimera. Chimeric brindles are often striped over their entire bodies, including the face and legs. Different colored stripes will have different DNA since they are the visual result of two zygotes combining shortly after conception.
An interesting example of breeding two brindle chimeras, Dunbars Gold and Sharp One, was published by AQHA in 2006. AQHA has since removed the story from their website, so scans of the original publication are borrowed from Sharp One owner Denise Charpilloz's website; read it here.
Dunbars Gold, a chimeric AQHA stallion (registered as red dun), pictured as a 2-year-old and an adult. He is the result of fused male and female fraternal twins; however, his reproductive organs are all male.
Sharp One, a chimeric AQHA mare (registered as red dun). She is the result of two female fraternal twins fusing in the womb. Her reproductive organs contain DNA from both twins, so she produces some eggs with one twin's DNA and some eggs with the other's DNA. This means that her foals can have genetically different mothers, despite being born from the same horse.
Sharp Barcoder, a sorrel (non-brindle) AQHA filly by Dunbars Gold out of Sharp One. Twice her parentage testing excluded Dunbars Gold as her sire and Sharp One as her dam; this anomaly led to the discovery that both of her parents were chimeras.
Chimeras are so rare that other explanations for brindle should be assumed first. Several other patterns can imitate chimeric brindle and can even be unpredictably heritable, such as sooty, grey, dun, extreme rabicano, and roan. These patterns can somehow be redistributed into vertical stripes, creating a brindle phenotype. These horses often have a false dorsal stripe not due to dun or nd1.
Tigresa Dash, a bay brindle Brazilian Quarter Horse mare, bred from imported AQHA. The dark face and diluted body color point to probable skewed dun.
FRS Reckless Dan, a grey brindle AQHA stallion. His stripes faded as his greying progressed. He was bred to Sharp One the year before Dunbars Gold; the resulting solid foal's parentage was verified by the parents' DNA on the first try. His stripes are likely skewed grey.
Sharp Trilogy, a chestnut-going-grey AQHA mare who did not show stripes until she started to go grey. Her brindle is likely due to skewed grey.
Riverdance's Marbled Tigress, a sooty smoky black roan Miniature Horse mare. Testing of her hair reveals that the striping is not due to chimerism. She was the first brindle to be registered with the American Miniature Horse Association.
KT Gun In A Million, a smoky black roan AQHA filly born with an odd brindle pattern that was found to be non-chimeric and likely due to drastically redistributed sooty countershading.
Natal Clasi, a bay Brazilian Warmblood stallion. He is often described as brindle, and may appear to be chimeric or "reverse brindle", but his skunk tail combined with the reports that all of his foals have had the same coloring point to probable extreme rabicano.
Catch A Bird, a bay TB stallion (NZ) known for his white stripes and (later) his roan foals. Despite the Jockey Club registering going-grey horses incorrectly as roans for years, a true roan TB had not existed before Catch A Bird's offspring. He is considered the source of the roan mutation in TB.
Patron Chico Lambedura, a bay brindle Criollo mare (described as "red zebra" in South America). Despite her parents being listed as a black overo sire and buckskin dam, her patterning is likely due to some sort of skewed roan. Note the symmetrical pattern on both sides of her body that stops at the points like a roan, and the way her hip brands have grown back solid bay, much like a corn mark on a roan.
Somatic mutations (mosaicism) can manifest as a white, striped phenotype, sometimes called reverse brindle or white brindle.
DA Remote Control, a bay ¾ Arabian- ¼ Hackney mare with a somatic mutation limited to her left side.
Remark, a bay TB filly with reverse brindle only on her right side.
