Post by Stella on Nov 1, 2010 20:05:55 GMT -5
info from
greenfield.fortunecity.com/dreams/799/hc/horsecolors.htm
Black
fc04.deviantart.net/fs45/i/2009/119/8/d/black_horse_by_loreeshell.jpg
Black is controlled by genes at the E locus. EE and Ee are black; ee is chestnut. All horses are genetically black or red (with red being chestnut/sorrel), and other genes modify the expression of those colors, diluting them, or adding white markings.
A black horse is black over its entire body, except for any white markings that may exist. Some horses that appear black have reddish-brown tinting in the hair around their muzzle, eye, flank, and behind the elbows. These horses are not black; they are usually called "seal brown" (more on this in the bay section). True chocolate brown -- not reddish-brown, but the color of a chocolate Labrador Retriever, with chocolate brown skin -- is extremely rare in the horse. The gene for this color is not present in most horse breeds.
There are two types of black. Ordinary black horses (top) will fade to a rusty brownish color (link) if the horse is exposed to sunlight on a regular basis. The other type of black is called jet black; it is a blue-black shade that is fadeproof.
Chestnut and Sorrel
Dark Chestnut- fc08.deviantart.net/fs18/i/2007/187/3/3/Chestnut_Arabian_11_by_littlenake.jpg
Red chestnut- fc03.deviantart.net/fs36/i/2008/278/c/4/Chestnut_Mare_by_extraordinaryxstock.jpg
Sorrel- fc04.deviantart.net/fs51/i/2009/274/e/b/Chestnut_Welsh_3_by_xrockinrobynstock.jpg [with flaxen mane But Liver pelt]
Liver Chestnut- fc09.deviantart.net/fs71/i/2010/050/1/7/liver_chestnut_side_profile_by_Chunga_Stock.jpg
Medium-light Chestnut- fc03.deviantart.net/fs71/i/2010/160/3/0/Chestnut_Arabian_Stock_2_by_Colourize_Stock.jpg
Chestnut and sorrel are essentially the same color, genetically speaking. These horses are red, yellowish red, or reddish brown, and they do not have black points (the points being the mane, tail, and lower legs). Chestnut and sorrel are determined by genes at the E locus. Horses that are ee at that locus are chestnut/sorrel; horses with an E gene at the locus are black (absent other modifiers). Chestnut is recessive to black, meaning that a chestnut bred to a chestnut will always produce a chestnut foal. Two blacks bred together can produce a chestnut foal if both blacks are heterozygous (Ee). In that mating, there's a 25% chance of a chestnut foal, and 75% chance of a black foal. A black horse who is heterozygous (EE) will only produce black foals.
The difference between chestnut and sorrel is somewhat controversial. Some people call the redder versions sorrel; some call the redder versions chestnut. Some people (such as me) call the horses with flaxen manes and tails sorrel; some do not. Some people use one term or the other for all red horses. Some consider sorrel a term for horses who are ridden western, reserving chestnut for horses ridden English. Some breed registries use only chestnut or only sorrel; some use both.
[Sorrel]
Some chestnuts (I call them sorrels) have flaxen manes and tails. This is caused by the recessive gene f, which, in the heterozygous state, lightens the color of the points. The genotype of a horse with a flaxen mane and tail, such as the horses below, is eeff, while a chestnut without a flaxen mane and tail, like the horses in the photos above, is eeF-.
Some sorrels are very light in color and are often mistaken for palominos, but a true palomino has no reddish cast to its coat.
Bay[blood, mahogany or light bay]
Bay horses are identified by having a reddish brown body and black points (mane, tail, lower legs). The bay color is caused by genes at two different loci, A and E. The presence of the E gene codes for black color, and the A gene restricts the black color to the points. So bay horses are called A-E-.
Black horses have no A gene; they are aa at the A locus. Their genotype is aaE-. Lack of the A gene allows the black color to "spread" over the entire body; the presence of the A gene restricts the black color to the points.
Chestnut horses can carry the A gene, but since they have no black pigment (ee), they will not display evidence of the A gene if they carry it. An aaee horse and an A-ee horse look the same; both are simply chestnut. An A-ee chestnut can, if bred to a black (aaE-), produce a bay foal (A-E-), if the black parent passes on one of its E genes.
[brown]Breed registries, being political organizations, enjoy defining their own terms. Some registries, such as the Jockey Club, which registers Thoroughbreds, have a color they actually call "dark bay or brown." This ambiguously refers to any dark but nonblack horse with black points. A really dark A-E-, in other words. As I mentioned in the black section, true chocolate brown with no reddish cast is extremely rare in the horse. I do not have a photo of a horse this color. But when horsepeople refer to a horse as "brown," they usually mean one that looks like this:
fc02.deviantart.net/fs26/i/2008/089/c/a/Dressage___tackless___by_rachellafranchistock.jpg
Dun
Dun is a dilution color. It is caused by the dun gene, D, diluting what would otherwise be a bay horse. It dilutes the reddish brown of the bay's body color to a yellowish color, and adds primitive markings or dun factors. These consist of a dorsal stripe and horizontal "zebra stripes" on the upper legs, and can also include a transverse stripe over the withers and markings on the ears.
A dun horse's genotype is A-E-D-, with E causing black color, A restricting it to the points, and D diluting the body color from red to yellow and adding dun factors.
D will also dilute otherwise black and chestnut horses, causing them to be grulla or red dun respectively. Those colors are featured on their own pages. Regular dun, featured on this page, is is often called "zebra dun" to differentiate it from the other types of dun.
Red Dun
Red dun (D-ee) is a di
luted form of chestnut. The body color of the red dun is a pale, washed-out yellowish red, and the point color is red, in various shades. Like all members of the dun family, primitive markings are present. Like most colors, red dun comes in a variety of shades. The horse above is pretty light (a shade often called orange dun), whereas the horse at right is rather dark. Some chestnuts are so light that they are lighter than some shades of red dun. The difference, of course, is that the points of the red dun are darker than its body color, and the red dun, like all duns, has primitive markings (usually hard to see in photos!).
Grulla
Grulla (pronounced "grew-yah," and also spelled grullo) is a slate or slate-brown color with black points and primitive markings (dorsal stripe, leg stripes, etc.). The horse also has a black face. Grulla is black diluted by the D gene, or aaD-E-. Unlike a grey or roan horse, the hairs of a grulla are all individually slate-colored. Greys and roans have colored hairs intermixed with white hairs.
Grulla comes in many shades, some light, some dark, some silvery, some olive-colored. All have black points, black masks, and primitive markings.
Palomino
Palommino is a dilution of chestnut by one copy of the c gene (Ccee). Palominos feature a gold, yellow, or tan body, and a white or off-white mane and tail.
Palomino is a popular color among horsemen and lay people alike. It has spawned the creation of a few color registries, chiefly the Palomino Horse Breeders of America. Since palomino requires a heterozygous arrangement of alleles at the C locus (the homozygous dominant CC will be chestnut, and the homozygous recessive cc will be cremello), palominos cannot breed true -- in other words, crossing a palomino with a palomino will only give you a 50% chance of a palomino foal, with a 25% chance of a chestnut and 25% chance of a cremello. The inheritance section shows a demonstration of this.
Dunalino
The two photos below are of a filly whose color is popularly called "dunalino." A dunalino horse has inherited the genes for red dun and palomino; their genotype is CcD-ee. Since different genes cause these two colors, it is possible for a horse to inherit both types. This filly does have primitive markings, although you can't see them in these pictures, and her legs are a darker shade than her body color, as befits her red dun genes. But her body is a gold color and her mane and tail are white, as befits a palomino. Any palomino with primitive markings can be called a dunalino, but breed registries will call them palominos.
Bucksin
Buckskin (A-CcE-) is bay diluted by the heterozygous effect of the c dilution gene. These horses are yellow, tan, or gold, with black points. Buckskin is similar to dun, but does not have primitive markings.
In the interest of clear terminology, I have to work in a little bit of politics here. Like dark brown vs. bay and chestnut vs. sorrel, buckskin vs. dun is a little controversial. Most people define buckskin the way I did above, but some reserve the term "buckskin" for buckskins or duns that are light in shade, whether they have primitive markings or not. But since the two colors are genetically distinct (A-CCD-E for primitive-marked duns and A-CcddE- for non-primitive-marked buckskins), there is little point in trying to differentiate them by degree of shading, since that's always subject to interpretation by the human eye.
Further complicating the issue is the existence of two color registries, the American Buckskin Registry Association and the International Buckskin Horse Association. Although buckskin, dun, and grulla are colors, not breeds, you can create a registry for just about anything and define your terms any way you want. ABRA and IBHA call "buckskins" almost any type of dilute except palomino (which has its own set of registries and controversies). ABRA and IBHA will register any buckskin, dun, red dun, or grulla, and if so registered, the horse becomes a Buckskin (capital B) and can be exhibited in Buckskin shows (i.e., shows affiliated with ABRA or IBHA). Calling such a horse a Buckskin does not make the horse buckskin-colored, it just means the horse is registered with one or both of those associations.
Cremellos && Perlinos
cremello
perlino
Most animal species have a gene that codes for albinism. The horse, however, does not possess the albino gene. There are white and white-appearing horses, but these are not albinos. Most have some pigment, and all have brown or blue eyes instead of the pink eye of the true albino.
A cremello has a cream-colored coat, a white mane and tail, pink skin, and blue eyes. A perlino has a cream-colored coat, reddish-tinted points (mane, tail, lower legs), pink skin, and blue eyes.
The cremello genotype is ccee. They are often called "double-diluted palominos" because they have two copies of the c dilution gene. Perlinos are A-ccE-. They are the only color to possess of the A and E genes and not have black points. The effect of cc is to dilute the black points to a rusty color. (See the dilutes page for further information and illustrations of the effect of Cc and cc on bay and chestnut.)
Silver Dapple
Silver dapple is caused by the Z gene, which dilutes black to a flat brown color, usually with dapples, and changes the mane and tail to white. The horse also has a dark mask on its face. (Despite its name, this color is not related at all to dapple grey.)
The silver dapple genotype is aaE-Z-.
As you can see from these pictures, some silver dapples are actually dappled, while some aren't. Because the dapples are usually present, all horses this color are called silver dapple, regardless of the presence of actual dapples.
Greys
Grey is a pattern of individual white hairs intermingled with colored hairs. It can occur on any base color. Grey foals are born colored and become progressively lighter with age until the horse appears white, but the grey horse retains its dark skin, unlike a true white horse, which has pink skin.
Grey is caused by a dominant gene, G. GG and Gg horses are grey; gg horses are not.
Roan
Red and blue roan
Roan is similar to grey in that it is a pattern of individual white hairs sprinkled into the coat. Unlike grey, roan horses are born roan and stay the same color throughout their lives (although they may appear lighter or darker in their winter coats). Also, the head, legs, mane and tail of a roan horse are solid-colored and do not display "roaning." This makes roan easy to distinguish from grey, since the face of a grey horse is the first part of the body that begins to lighten.
Roan can occur on any base color and is caused by the dominant gene R. Homozygous roan (RR) is believed to be lethal; the foal that inherits an R gene from each parent probably does not survive, with a few exceptions. Almost all roan horses are heterozygous Rr, while rr horses are nonroan.
Since roan can occur combined with any color, the appearance of roan horses varies greatly. The common shades of roan are blue roan (roan on black), red roan (roan on bay), and strawberry roan (roan on chestnut).
Rabicano
Rabicano is a pattern of white hairs that's similar to roan. It consists of white hairs on the flanks of the horse and at the top of the tail. The white hairs on the flanks often spread onto the rib area, where they take on a vertical striping appearance.
Rabicano is caused by the dominant gene Rb.
Tobiano[paint horse]
Tobiano is a pinto pattern caused by the T gene. It's a dominant gene; TT and Tt are tobiano, while tt is not. Tobiano can be distinguished from other pinto patterns because a tobiano horse has white that crosses its spine somewhere between the withers and the tail (topline), as if the white had been poured on from above. Tobianos also almost always have white stockings on all four legs; often the white socks blend into the white on the body. A solid-colored leg on a tobiano is almost unheard of.
Overo
Overo is a pinto pattern caused by the dominant gene O. Overo was formerly thought to be recessive, but statistic analysis of the offspring of overo horses has proven it to be a dominant. Like roan, homozygous OO overo is a lethal; foals who inherit an O gene from each parent usually die in utero or shortly after birth. So almost all overos are heterozygous Oo, with oo horses being non-overo.
Overo is different from tobiano in that the white markings of an overo horse do not cross the topline. Instead, they appear to begin at the belly and spread upward. White legs are not as common in the overo as they are in the tobiano, and there is often a great deal of white on the face. The horse in the photo above is a dark chestnut overo. Note the lack of white crossing the topline, the one solid-colored leg, and the large amount of white on the face. These are all hallmarks of the overo.
Sabino
Sabino is a pinto pattern often confused with overo. It differs from overo in these ways:
-- The edges of the white areas of a sabino are jagged, feathery, or "roaned." The edges of the white areas of an overo are more crisp.
-- Sabinos often have a white feathery-edged patch underneath their throat. Overos don't necessarily have this.
-- Sabinos rarely have blue eyes. Overos often do.
-- Sabinos often have hind stockings in which the white area seeps up the front side of the leg; also, if they have no white stockings on their forelegs, they often have a white patch on the knee.
Sabino is caused by the dominant gene Sb. Homozygous SbSb horses are often almost solid white; heterozygous Sbsb horses display "normal" sabino patterning, and homozygous sbsb horses are not sabino. There is no lethal factor associated with the sabino gene.
Blue eyes are also common in overos, while tobianos usually have brown eyes.
Splashed White
Splashed white is another pattern that's often confused with overo. Its characteristics are a white belly and legs, white on the back of the butt, and a white face with blue eyes. Yes, that sounds remarkably like overo, but overos usually do not have white legs.
Splashed white is caused by a dominant gene, Spl.
Appaloosa
bLANKET
Leopard
Appaloosa patterning is found in a number of breeds. Not every horse that looks like an Appaloosa is one, and not all registered Appaloosas have appaloosa markings, since the patterns do not breed true. In fact, the genetics for these patterns are not fully understood yet, so I'm not going to enumerate them.
There are four basic appaloosa patterns:
* Blanket: A colored horse with a white area over the hips, sometimes extending onto the back and sides.
* Leopard: A white horse with colored spots all over.
* Varnish roan. This is like regular roan, with two exceptions: The roaning extends onto the head of the horse, and there are colored (nonroan) patches on certain parts of the head and body (more on this later).
* Snowflake. This is a colored horse with white spots in random places on the body.
All of these factors, and others which alter the appearance of the horse, are inherited separately, so a horse can display more than one, such as varnish roan with a blanket. Appaloosas also often have vertically striped hooves, mottled pink-and-black skin, and visible sclera on the eyes.
greenfield.fortunecity.com/dreams/799/hc/horsecolors.htm
Black
fc04.deviantart.net/fs45/i/2009/119/8/d/black_horse_by_loreeshell.jpg
Black is controlled by genes at the E locus. EE and Ee are black; ee is chestnut. All horses are genetically black or red (with red being chestnut/sorrel), and other genes modify the expression of those colors, diluting them, or adding white markings.
A black horse is black over its entire body, except for any white markings that may exist. Some horses that appear black have reddish-brown tinting in the hair around their muzzle, eye, flank, and behind the elbows. These horses are not black; they are usually called "seal brown" (more on this in the bay section). True chocolate brown -- not reddish-brown, but the color of a chocolate Labrador Retriever, with chocolate brown skin -- is extremely rare in the horse. The gene for this color is not present in most horse breeds.
There are two types of black. Ordinary black horses (top) will fade to a rusty brownish color (link) if the horse is exposed to sunlight on a regular basis. The other type of black is called jet black; it is a blue-black shade that is fadeproof.
Chestnut and Sorrel
Dark Chestnut- fc08.deviantart.net/fs18/i/2007/187/3/3/Chestnut_Arabian_11_by_littlenake.jpg
Red chestnut- fc03.deviantart.net/fs36/i/2008/278/c/4/Chestnut_Mare_by_extraordinaryxstock.jpg
Sorrel- fc04.deviantart.net/fs51/i/2009/274/e/b/Chestnut_Welsh_3_by_xrockinrobynstock.jpg [with flaxen mane But Liver pelt]
Liver Chestnut- fc09.deviantart.net/fs71/i/2010/050/1/7/liver_chestnut_side_profile_by_Chunga_Stock.jpg
Medium-light Chestnut- fc03.deviantart.net/fs71/i/2010/160/3/0/Chestnut_Arabian_Stock_2_by_Colourize_Stock.jpg
Chestnut and sorrel are essentially the same color, genetically speaking. These horses are red, yellowish red, or reddish brown, and they do not have black points (the points being the mane, tail, and lower legs). Chestnut and sorrel are determined by genes at the E locus. Horses that are ee at that locus are chestnut/sorrel; horses with an E gene at the locus are black (absent other modifiers). Chestnut is recessive to black, meaning that a chestnut bred to a chestnut will always produce a chestnut foal. Two blacks bred together can produce a chestnut foal if both blacks are heterozygous (Ee). In that mating, there's a 25% chance of a chestnut foal, and 75% chance of a black foal. A black horse who is heterozygous (EE) will only produce black foals.
The difference between chestnut and sorrel is somewhat controversial. Some people call the redder versions sorrel; some call the redder versions chestnut. Some people (such as me) call the horses with flaxen manes and tails sorrel; some do not. Some people use one term or the other for all red horses. Some consider sorrel a term for horses who are ridden western, reserving chestnut for horses ridden English. Some breed registries use only chestnut or only sorrel; some use both.
[Sorrel]
Some chestnuts (I call them sorrels) have flaxen manes and tails. This is caused by the recessive gene f, which, in the heterozygous state, lightens the color of the points. The genotype of a horse with a flaxen mane and tail, such as the horses below, is eeff, while a chestnut without a flaxen mane and tail, like the horses in the photos above, is eeF-.
Some sorrels are very light in color and are often mistaken for palominos, but a true palomino has no reddish cast to its coat.
Bay[blood, mahogany or light bay]
Bay horses are identified by having a reddish brown body and black points (mane, tail, lower legs). The bay color is caused by genes at two different loci, A and E. The presence of the E gene codes for black color, and the A gene restricts the black color to the points. So bay horses are called A-E-.
Black horses have no A gene; they are aa at the A locus. Their genotype is aaE-. Lack of the A gene allows the black color to "spread" over the entire body; the presence of the A gene restricts the black color to the points.
Chestnut horses can carry the A gene, but since they have no black pigment (ee), they will not display evidence of the A gene if they carry it. An aaee horse and an A-ee horse look the same; both are simply chestnut. An A-ee chestnut can, if bred to a black (aaE-), produce a bay foal (A-E-), if the black parent passes on one of its E genes.
[brown]Breed registries, being political organizations, enjoy defining their own terms. Some registries, such as the Jockey Club, which registers Thoroughbreds, have a color they actually call "dark bay or brown." This ambiguously refers to any dark but nonblack horse with black points. A really dark A-E-, in other words. As I mentioned in the black section, true chocolate brown with no reddish cast is extremely rare in the horse. I do not have a photo of a horse this color. But when horsepeople refer to a horse as "brown," they usually mean one that looks like this:
fc02.deviantart.net/fs26/i/2008/089/c/a/Dressage___tackless___by_rachellafranchistock.jpg
Dun
Dun is a dilution color. It is caused by the dun gene, D, diluting what would otherwise be a bay horse. It dilutes the reddish brown of the bay's body color to a yellowish color, and adds primitive markings or dun factors. These consist of a dorsal stripe and horizontal "zebra stripes" on the upper legs, and can also include a transverse stripe over the withers and markings on the ears.
A dun horse's genotype is A-E-D-, with E causing black color, A restricting it to the points, and D diluting the body color from red to yellow and adding dun factors.
D will also dilute otherwise black and chestnut horses, causing them to be grulla or red dun respectively. Those colors are featured on their own pages. Regular dun, featured on this page, is is often called "zebra dun" to differentiate it from the other types of dun.
Red Dun
Red dun (D-ee) is a di
luted form of chestnut. The body color of the red dun is a pale, washed-out yellowish red, and the point color is red, in various shades. Like all members of the dun family, primitive markings are present. Like most colors, red dun comes in a variety of shades. The horse above is pretty light (a shade often called orange dun), whereas the horse at right is rather dark. Some chestnuts are so light that they are lighter than some shades of red dun. The difference, of course, is that the points of the red dun are darker than its body color, and the red dun, like all duns, has primitive markings (usually hard to see in photos!).Grulla
Grulla (pronounced "grew-yah," and also spelled grullo) is a slate or slate-brown color with black points and primitive markings (dorsal stripe, leg stripes, etc.). The horse also has a black face. Grulla is black diluted by the D gene, or aaD-E-. Unlike a grey or roan horse, the hairs of a grulla are all individually slate-colored. Greys and roans have colored hairs intermixed with white hairs.
Grulla comes in many shades, some light, some dark, some silvery, some olive-colored. All have black points, black masks, and primitive markings.
Palomino
Palommino is a dilution of chestnut by one copy of the c gene (Ccee). Palominos feature a gold, yellow, or tan body, and a white or off-white mane and tail.
Palomino is a popular color among horsemen and lay people alike. It has spawned the creation of a few color registries, chiefly the Palomino Horse Breeders of America. Since palomino requires a heterozygous arrangement of alleles at the C locus (the homozygous dominant CC will be chestnut, and the homozygous recessive cc will be cremello), palominos cannot breed true -- in other words, crossing a palomino with a palomino will only give you a 50% chance of a palomino foal, with a 25% chance of a chestnut and 25% chance of a cremello. The inheritance section shows a demonstration of this.
Dunalino
The two photos below are of a filly whose color is popularly called "dunalino." A dunalino horse has inherited the genes for red dun and palomino; their genotype is CcD-ee. Since different genes cause these two colors, it is possible for a horse to inherit both types. This filly does have primitive markings, although you can't see them in these pictures, and her legs are a darker shade than her body color, as befits her red dun genes. But her body is a gold color and her mane and tail are white, as befits a palomino. Any palomino with primitive markings can be called a dunalino, but breed registries will call them palominos.
Bucksin
Buckskin (A-CcE-) is bay diluted by the heterozygous effect of the c dilution gene. These horses are yellow, tan, or gold, with black points. Buckskin is similar to dun, but does not have primitive markings.
In the interest of clear terminology, I have to work in a little bit of politics here. Like dark brown vs. bay and chestnut vs. sorrel, buckskin vs. dun is a little controversial. Most people define buckskin the way I did above, but some reserve the term "buckskin" for buckskins or duns that are light in shade, whether they have primitive markings or not. But since the two colors are genetically distinct (A-CCD-E for primitive-marked duns and A-CcddE- for non-primitive-marked buckskins), there is little point in trying to differentiate them by degree of shading, since that's always subject to interpretation by the human eye.
Further complicating the issue is the existence of two color registries, the American Buckskin Registry Association and the International Buckskin Horse Association. Although buckskin, dun, and grulla are colors, not breeds, you can create a registry for just about anything and define your terms any way you want. ABRA and IBHA call "buckskins" almost any type of dilute except palomino (which has its own set of registries and controversies). ABRA and IBHA will register any buckskin, dun, red dun, or grulla, and if so registered, the horse becomes a Buckskin (capital B) and can be exhibited in Buckskin shows (i.e., shows affiliated with ABRA or IBHA). Calling such a horse a Buckskin does not make the horse buckskin-colored, it just means the horse is registered with one or both of those associations.
Cremellos && Perlinos
cremello
perlino
Most animal species have a gene that codes for albinism. The horse, however, does not possess the albino gene. There are white and white-appearing horses, but these are not albinos. Most have some pigment, and all have brown or blue eyes instead of the pink eye of the true albino.
A cremello has a cream-colored coat, a white mane and tail, pink skin, and blue eyes. A perlino has a cream-colored coat, reddish-tinted points (mane, tail, lower legs), pink skin, and blue eyes.
The cremello genotype is ccee. They are often called "double-diluted palominos" because they have two copies of the c dilution gene. Perlinos are A-ccE-. They are the only color to possess of the A and E genes and not have black points. The effect of cc is to dilute the black points to a rusty color. (See the dilutes page for further information and illustrations of the effect of Cc and cc on bay and chestnut.)
Silver Dapple
Silver dapple is caused by the Z gene, which dilutes black to a flat brown color, usually with dapples, and changes the mane and tail to white. The horse also has a dark mask on its face. (Despite its name, this color is not related at all to dapple grey.)
The silver dapple genotype is aaE-Z-.
As you can see from these pictures, some silver dapples are actually dappled, while some aren't. Because the dapples are usually present, all horses this color are called silver dapple, regardless of the presence of actual dapples.
Greys
Grey is a pattern of individual white hairs intermingled with colored hairs. It can occur on any base color. Grey foals are born colored and become progressively lighter with age until the horse appears white, but the grey horse retains its dark skin, unlike a true white horse, which has pink skin.
Grey is caused by a dominant gene, G. GG and Gg horses are grey; gg horses are not.
Roan
Red and blue roan
Roan is similar to grey in that it is a pattern of individual white hairs sprinkled into the coat. Unlike grey, roan horses are born roan and stay the same color throughout their lives (although they may appear lighter or darker in their winter coats). Also, the head, legs, mane and tail of a roan horse are solid-colored and do not display "roaning." This makes roan easy to distinguish from grey, since the face of a grey horse is the first part of the body that begins to lighten.
Roan can occur on any base color and is caused by the dominant gene R. Homozygous roan (RR) is believed to be lethal; the foal that inherits an R gene from each parent probably does not survive, with a few exceptions. Almost all roan horses are heterozygous Rr, while rr horses are nonroan.
Since roan can occur combined with any color, the appearance of roan horses varies greatly. The common shades of roan are blue roan (roan on black), red roan (roan on bay), and strawberry roan (roan on chestnut).
Rabicano
Rabicano is a pattern of white hairs that's similar to roan. It consists of white hairs on the flanks of the horse and at the top of the tail. The white hairs on the flanks often spread onto the rib area, where they take on a vertical striping appearance.
Rabicano is caused by the dominant gene Rb.
Tobiano[paint horse]
Tobiano is a pinto pattern caused by the T gene. It's a dominant gene; TT and Tt are tobiano, while tt is not. Tobiano can be distinguished from other pinto patterns because a tobiano horse has white that crosses its spine somewhere between the withers and the tail (topline), as if the white had been poured on from above. Tobianos also almost always have white stockings on all four legs; often the white socks blend into the white on the body. A solid-colored leg on a tobiano is almost unheard of.
Overo
Overo is a pinto pattern caused by the dominant gene O. Overo was formerly thought to be recessive, but statistic analysis of the offspring of overo horses has proven it to be a dominant. Like roan, homozygous OO overo is a lethal; foals who inherit an O gene from each parent usually die in utero or shortly after birth. So almost all overos are heterozygous Oo, with oo horses being non-overo.
Overo is different from tobiano in that the white markings of an overo horse do not cross the topline. Instead, they appear to begin at the belly and spread upward. White legs are not as common in the overo as they are in the tobiano, and there is often a great deal of white on the face. The horse in the photo above is a dark chestnut overo. Note the lack of white crossing the topline, the one solid-colored leg, and the large amount of white on the face. These are all hallmarks of the overo.
Sabino
Sabino is a pinto pattern often confused with overo. It differs from overo in these ways:
-- The edges of the white areas of a sabino are jagged, feathery, or "roaned." The edges of the white areas of an overo are more crisp.
-- Sabinos often have a white feathery-edged patch underneath their throat. Overos don't necessarily have this.
-- Sabinos rarely have blue eyes. Overos often do.
-- Sabinos often have hind stockings in which the white area seeps up the front side of the leg; also, if they have no white stockings on their forelegs, they often have a white patch on the knee.
Sabino is caused by the dominant gene Sb. Homozygous SbSb horses are often almost solid white; heterozygous Sbsb horses display "normal" sabino patterning, and homozygous sbsb horses are not sabino. There is no lethal factor associated with the sabino gene.
Blue eyes are also common in overos, while tobianos usually have brown eyes.
Splashed White
Splashed white is another pattern that's often confused with overo. Its characteristics are a white belly and legs, white on the back of the butt, and a white face with blue eyes. Yes, that sounds remarkably like overo, but overos usually do not have white legs.
Splashed white is caused by a dominant gene, Spl.
Appaloosa
bLANKET LeopardAppaloosa patterning is found in a number of breeds. Not every horse that looks like an Appaloosa is one, and not all registered Appaloosas have appaloosa markings, since the patterns do not breed true. In fact, the genetics for these patterns are not fully understood yet, so I'm not going to enumerate them.
There are four basic appaloosa patterns:
* Blanket: A colored horse with a white area over the hips, sometimes extending onto the back and sides.
* Leopard: A white horse with colored spots all over.
* Varnish roan. This is like regular roan, with two exceptions: The roaning extends onto the head of the horse, and there are colored (nonroan) patches on certain parts of the head and body (more on this later).
* Snowflake. This is a colored horse with white spots in random places on the body.
All of these factors, and others which alter the appearance of the horse, are inherited separately, so a horse can display more than one, such as varnish roan with a blanket. Appaloosas also often have vertically striped hooves, mottled pink-and-black skin, and visible sclera on the eyes.
