Post by Carole on Jan 18, 2006 15:48:41 GMT -5
I found this site while surfing and decided to copy some of the info since i had asked about it myself.
The Basics of Equine Color Genetics
The Foundations: I find that the easiest way to think about horse color is to imagine it as a series of building blocks. Each color is built from a group of genes that act differently when combined with different bases. One key thing to understand is that horses inherit color genes from each parent---each parent has several pairs of color genes, and half of each pair is passed on to the foal.
All horse colors are built on two base colors, black (E) and chestnut (e). Black is dominant to chestnut, and chestnut is recessive to all colors. That means that a horse carrying 2 black genes (EE) will be (homozygous) black; a horse carrying one black gene and one chestnut gene (Ee) will also be black (but heterozygous); and a horse carrying two chestnut genes (ee) will be chestnut (always homozygous). So if two heterozygous black horses are bred together (Ee +Ee), they have 1 chance in 4 of producing a homozygous black (EE), 2 chances in 4 of producing a heterozygous black (Ee), and 1 chance in 4 of producing a chestnut. Pretty neat, huh? Two chestnuts bred together (ee + ee) can only produce chestnut.
Chestnuts vary in shade in from a light golden color to red to liver. Some even have have flaxen manes and tails.
Black horses can also vary shade---from blue-black to dusty black to sun-faded black. Not all black horses fade in the sun, but those that do generally resemble brown horses.
The Dilution Genes
Agouti, Cream, Dun, Roan, Silver Dapple, Champagne
Many horse colors are the result of dilution genes acting on the base colors. They all work similarly in that they dilute the main body color, but usually not the color of the legs, mane, and tail. Bay is the most basic dilution color, and it is caused by the agouti gene diluting black. The black body hairs are diluted to a shade of brown while the legs, mane, and tail remain black. Like most dilution genes, agouti is dominant, so if a horse carries it, it will be expressed.
Agouti is not actually a seperate gene, but rather a piece of the black gene called an allele. It can occur in three forms: A-agouti (meaning the horse is bay), a-non agouti (meaning the horse remains black), and At-brown (a color often confused with dark bay, but genetically different from bay).
Brown is also a dilution that acts on black as I mentioned above. Though it looks similar to dark bay, it is genetically different. Brown horses are characterized by having a black coat with brown hairs on their muzzles, flanks, inner forearms, and inner thighs. Seattle Slew is an excellent example of this color
Cream: Unlike agouti, which can only act on the black gene, cream can modify any color it acts in conjunction with, though it is most commonly seen combined with chestnut, bay, and black. The cream gene is an incomplete dominant, meaning it is always expressed when it's present, but it acts differently in its heterozygous (1 copy of the gene) and homozygous (2 copies of the gene) states. Simply put, horses with one copy of the cream gene will have a diluted coat; horses with 2 copies will have a doubly diluted coat. Double dilutes always have blue eyes. The cream gene does not effect black hairs in it's single form, only in it's double form.
Palomino: Chestnut + 1 Cream gene
Chestnuts have no black hairs, so the entire coat is diluted. The mane and tail are always white
Cremello: Chestnut + 2 Cream genes
Cremello is basically a very pale palomino color---white markings are still discernable against the pale cream colored coat. Cremellos have blue eyes and light colored skin. (The only true pink skin is under white markings.)
Buckskin: Bay + 1 Cream gene
Because the cream gene doesn't affect black hairs, the dark points remain even after the bay body color has been diluted.
Perlino: Bay + 2 Cream genes
When two cream genes are present, the body color becomes very pale, and the black points are diluted to a red or brown color.
Smoky Black: Black + 1 Cream gene
The cream gene has very little affect on black hairs in it's single state, so smoky black is very hard to distinguish from brown or (very sooty) dark bays. Often the best way to tell if the horse carries the cream gene is to breed it. If it produces cream offspring from non-cream carrying mates, or double dilution creams from cream carrying mates, then you'll know it's a smoky black
Smoky Cream: Black + 2 Cream genes
This Akhal Teke is thought to be a smoky cream. Notice how his points are still a darker shade than the rest of the body
Dun: Like the cream gene, the dun gene is also a dilution gene, but it is a complete dominant rather than an incomplete one, meaning heterozygous and homozygous duns look the same. It is often considered a "primitive" color because most very ancient breeds are predominantly or entirely dun, i.e. Przewalskis, Tarpans, etc. Duns are characterized by certain markings known as dun factors. They usually consist of a distinct dorsal (or eel) stripe down the back, leg barring (or zebra stripes), and cobwebbing on the face. As with the cream gene, the dun gene only dilutes the body color, not the points.
Red Dun: Chestnut + Dun
The chestnut color is diluted to a sandy color, but the mane, tail, and points remain chestnut. The dun factors tend to be the same reddish brown color as the points
Bay Dun: Bay + Dun
The body color is diluted to a sandy color, but the points remain dark. This mustang shows another typical characteristic of duns---the light colored hairs on top of the mane and at the dock of the tail
Black Roan: Black + Roan
The black coat is sprinkled with white hairs except on the head, legs, mane, and tail. Sometimes called a blue roan.
Silver Dapple: Silver dapple is a dilution gene that only affects black (and thus bay), but not chestnut. It acts by changing black pigment to a chocolately color, and bay to a reddish, sometimes dappled color. (This dappling is unrelated to that caused by the grey gene.) While the legs are not affected by the silver dapple gene, the mane and tail change to a pale, flaxen color. Because of this, flaxen chestnuts are easily confused with silver dapple chestnuts. This color is found primarily in Rocky Mountain Horses, other related gaited horses, Mustangs, and Shetland Ponies.
Champagne: The champagne gene is a simple dominant dilution gene, much like dun. In other words, if a horse carries the champagne gene, he will be champagne in color. Champagne combined with chestnut is called "gold," with bay is "amber," and with black is "classic." Sometimes, champagne is combined with the cream gene as well, producing a color known as "ivory." It is known to act in conjunction with other dilution genes (i.e. dun), but those colors have yet to be named. Champagne horses are usually born with bright pink skin that becomes mottled as they age. They are also born with blue eyes that change to a hazel shade as they get older. The champagne gene is found most often in Tennessee Walking Horses, Missouri Foxtrotters, American Saddlebreds, and Quarter Horses. The best resource for more information and pictures of champagne horses is the Champagne Horse Association
Gold Champagne: Chestnut + Champagne
The chestnut color is diluted to a golden color, similar to palomino. There is a distinguisihable difference because champagnes have hazel eyes and mottled skin. Many champagnes have a metallic or pearly sheen to their coats.
Amber Champagne: Bay + Champagne
The bay color is diluted to a golden color, similar to buckskin, but again is distinguishable because of the hazel eyes and mottled skin
Classic Champagne: Black + Champagne
The black color is diluted to a sort of mousie grey-brown shade with darker points. Just like the gold and amber champagnes, classic horses have the telltale hazel eyes and mottle skin.
When combined with the creme gene, champagne horses are diluted to a nearly white shade called ivory champagne. Only classic champagnes combined with cream retain any noticeably dark pigment in their mane and tail and legs.
Modifiers
Grey
Grey: Contrary to popular belief, grey is not so much a color as it is a pattern (or more accurately still, a color modifier). Grey is a dominant gene that causes the horse's natural coat color, whether it be bay, black, dun, or palomino roan, to slowly "depigment" as the horse ages, much like human hair "greys out" with age. Most greys go through a lovely dappled phase, ending up nearly white or sometimes fleabitten. Because grey is a dominant "color," all grey horses will have at least one grey parent. Foals usually show evidence of greying on their faces first, particularly around the eyes. Holy Bull, exhibited the changes a grey goes through,his face had already lightened in color even though the rest of his coat is still relatively dark .
Miscellaneous Modifiers
Rabicano, Brindle, Birdcatcher Spots, Chubari Spots, Bend Or Spots, and Sooty
Rabicano: Rabicano is a pattern that is often confused with true dark-headed roan. The rabicano gene, however, is entirely seperate from the roan gene, though it does create a pattern of white hairs that can be similar to roan. It is usually manifested as a sprinkling of white hairs radiating out from the horses flank, sometimes spreading across the barrel and onto the neck. Rabicanos also have a white-topped tail, known as a coon tail or skunk tail. There is some thought that rabicano may be tied to or somehow related to sabino as the rabicano pattern is often found in conjunction with sabino. Rabicano can act an any coat color.
Brindle: Brindle is an unusual pattern of dark, vertical lines on a lighter-colored coat. Though it is seen in a variety of breeds, it is quite rare. The genetics of brindle are unknown, but according to Dr. Philip Sponenberg, a long-time student of equine color genetics, "brindle seems to require sooty black countershading for its expression, and reorganizes sootiness into vertical stripes instead of a more uniform sprinkling of hairs."
Seeing Spots: A variety of non-Appaloosa spots do occur in many breeds. Birdcatcher spots, named for the Thoroughbred stallion who exhibited them, are small white spots scattered throughout a horse's coat. In many cases, the spots appear and grow in number for a period of years, and then gradually fade away. Sometimes, the spots will persist throughout a horse's lifetime. Chubari spots are similar, but are usually larger, often egg-shaped and egg-sized. They seem to occur most frequently on grey coats, and of course, fade as the grey coat fades. Most grey TBs and grey horses with TB breeding can trace their spots back to The Tetrarch, a brilliant racehorse in England in the early 20th century. Bend Or spots are also named for the TB stallion who bore them. They are random dark spots on a lighter coat, often seen on chestnuts and palominos. They vary in size, sometimes only dime-sized, and sometimes as big as an outspread palm.
The Basics of Equine Color Genetics
The Foundations: I find that the easiest way to think about horse color is to imagine it as a series of building blocks. Each color is built from a group of genes that act differently when combined with different bases. One key thing to understand is that horses inherit color genes from each parent---each parent has several pairs of color genes, and half of each pair is passed on to the foal.
All horse colors are built on two base colors, black (E) and chestnut (e). Black is dominant to chestnut, and chestnut is recessive to all colors. That means that a horse carrying 2 black genes (EE) will be (homozygous) black; a horse carrying one black gene and one chestnut gene (Ee) will also be black (but heterozygous); and a horse carrying two chestnut genes (ee) will be chestnut (always homozygous). So if two heterozygous black horses are bred together (Ee +Ee), they have 1 chance in 4 of producing a homozygous black (EE), 2 chances in 4 of producing a heterozygous black (Ee), and 1 chance in 4 of producing a chestnut. Pretty neat, huh? Two chestnuts bred together (ee + ee) can only produce chestnut.
Chestnuts vary in shade in from a light golden color to red to liver. Some even have have flaxen manes and tails.
Black horses can also vary shade---from blue-black to dusty black to sun-faded black. Not all black horses fade in the sun, but those that do generally resemble brown horses.
The Dilution Genes
Agouti, Cream, Dun, Roan, Silver Dapple, Champagne
Many horse colors are the result of dilution genes acting on the base colors. They all work similarly in that they dilute the main body color, but usually not the color of the legs, mane, and tail. Bay is the most basic dilution color, and it is caused by the agouti gene diluting black. The black body hairs are diluted to a shade of brown while the legs, mane, and tail remain black. Like most dilution genes, agouti is dominant, so if a horse carries it, it will be expressed.
Agouti is not actually a seperate gene, but rather a piece of the black gene called an allele. It can occur in three forms: A-agouti (meaning the horse is bay), a-non agouti (meaning the horse remains black), and At-brown (a color often confused with dark bay, but genetically different from bay).
Brown is also a dilution that acts on black as I mentioned above. Though it looks similar to dark bay, it is genetically different. Brown horses are characterized by having a black coat with brown hairs on their muzzles, flanks, inner forearms, and inner thighs. Seattle Slew is an excellent example of this color
Cream: Unlike agouti, which can only act on the black gene, cream can modify any color it acts in conjunction with, though it is most commonly seen combined with chestnut, bay, and black. The cream gene is an incomplete dominant, meaning it is always expressed when it's present, but it acts differently in its heterozygous (1 copy of the gene) and homozygous (2 copies of the gene) states. Simply put, horses with one copy of the cream gene will have a diluted coat; horses with 2 copies will have a doubly diluted coat. Double dilutes always have blue eyes. The cream gene does not effect black hairs in it's single form, only in it's double form.
Palomino: Chestnut + 1 Cream gene
Chestnuts have no black hairs, so the entire coat is diluted. The mane and tail are always white
Cremello: Chestnut + 2 Cream genes
Cremello is basically a very pale palomino color---white markings are still discernable against the pale cream colored coat. Cremellos have blue eyes and light colored skin. (The only true pink skin is under white markings.)
Buckskin: Bay + 1 Cream gene
Because the cream gene doesn't affect black hairs, the dark points remain even after the bay body color has been diluted.
Perlino: Bay + 2 Cream genes
When two cream genes are present, the body color becomes very pale, and the black points are diluted to a red or brown color.
Smoky Black: Black + 1 Cream gene
The cream gene has very little affect on black hairs in it's single state, so smoky black is very hard to distinguish from brown or (very sooty) dark bays. Often the best way to tell if the horse carries the cream gene is to breed it. If it produces cream offspring from non-cream carrying mates, or double dilution creams from cream carrying mates, then you'll know it's a smoky black
Smoky Cream: Black + 2 Cream genes
This Akhal Teke is thought to be a smoky cream. Notice how his points are still a darker shade than the rest of the body
Dun: Like the cream gene, the dun gene is also a dilution gene, but it is a complete dominant rather than an incomplete one, meaning heterozygous and homozygous duns look the same. It is often considered a "primitive" color because most very ancient breeds are predominantly or entirely dun, i.e. Przewalskis, Tarpans, etc. Duns are characterized by certain markings known as dun factors. They usually consist of a distinct dorsal (or eel) stripe down the back, leg barring (or zebra stripes), and cobwebbing on the face. As with the cream gene, the dun gene only dilutes the body color, not the points.
Red Dun: Chestnut + Dun
The chestnut color is diluted to a sandy color, but the mane, tail, and points remain chestnut. The dun factors tend to be the same reddish brown color as the points
Bay Dun: Bay + Dun
The body color is diluted to a sandy color, but the points remain dark. This mustang shows another typical characteristic of duns---the light colored hairs on top of the mane and at the dock of the tail
Black Roan: Black + Roan
The black coat is sprinkled with white hairs except on the head, legs, mane, and tail. Sometimes called a blue roan.
Silver Dapple: Silver dapple is a dilution gene that only affects black (and thus bay), but not chestnut. It acts by changing black pigment to a chocolately color, and bay to a reddish, sometimes dappled color. (This dappling is unrelated to that caused by the grey gene.) While the legs are not affected by the silver dapple gene, the mane and tail change to a pale, flaxen color. Because of this, flaxen chestnuts are easily confused with silver dapple chestnuts. This color is found primarily in Rocky Mountain Horses, other related gaited horses, Mustangs, and Shetland Ponies.
Champagne: The champagne gene is a simple dominant dilution gene, much like dun. In other words, if a horse carries the champagne gene, he will be champagne in color. Champagne combined with chestnut is called "gold," with bay is "amber," and with black is "classic." Sometimes, champagne is combined with the cream gene as well, producing a color known as "ivory." It is known to act in conjunction with other dilution genes (i.e. dun), but those colors have yet to be named. Champagne horses are usually born with bright pink skin that becomes mottled as they age. They are also born with blue eyes that change to a hazel shade as they get older. The champagne gene is found most often in Tennessee Walking Horses, Missouri Foxtrotters, American Saddlebreds, and Quarter Horses. The best resource for more information and pictures of champagne horses is the Champagne Horse Association
Gold Champagne: Chestnut + Champagne
The chestnut color is diluted to a golden color, similar to palomino. There is a distinguisihable difference because champagnes have hazel eyes and mottled skin. Many champagnes have a metallic or pearly sheen to their coats.
Amber Champagne: Bay + Champagne
The bay color is diluted to a golden color, similar to buckskin, but again is distinguishable because of the hazel eyes and mottled skin
Classic Champagne: Black + Champagne
The black color is diluted to a sort of mousie grey-brown shade with darker points. Just like the gold and amber champagnes, classic horses have the telltale hazel eyes and mottle skin.
When combined with the creme gene, champagne horses are diluted to a nearly white shade called ivory champagne. Only classic champagnes combined with cream retain any noticeably dark pigment in their mane and tail and legs.
Modifiers
Grey
Grey: Contrary to popular belief, grey is not so much a color as it is a pattern (or more accurately still, a color modifier). Grey is a dominant gene that causes the horse's natural coat color, whether it be bay, black, dun, or palomino roan, to slowly "depigment" as the horse ages, much like human hair "greys out" with age. Most greys go through a lovely dappled phase, ending up nearly white or sometimes fleabitten. Because grey is a dominant "color," all grey horses will have at least one grey parent. Foals usually show evidence of greying on their faces first, particularly around the eyes. Holy Bull, exhibited the changes a grey goes through,his face had already lightened in color even though the rest of his coat is still relatively dark .
Miscellaneous Modifiers
Rabicano, Brindle, Birdcatcher Spots, Chubari Spots, Bend Or Spots, and Sooty
Rabicano: Rabicano is a pattern that is often confused with true dark-headed roan. The rabicano gene, however, is entirely seperate from the roan gene, though it does create a pattern of white hairs that can be similar to roan. It is usually manifested as a sprinkling of white hairs radiating out from the horses flank, sometimes spreading across the barrel and onto the neck. Rabicanos also have a white-topped tail, known as a coon tail or skunk tail. There is some thought that rabicano may be tied to or somehow related to sabino as the rabicano pattern is often found in conjunction with sabino. Rabicano can act an any coat color.
Brindle: Brindle is an unusual pattern of dark, vertical lines on a lighter-colored coat. Though it is seen in a variety of breeds, it is quite rare. The genetics of brindle are unknown, but according to Dr. Philip Sponenberg, a long-time student of equine color genetics, "brindle seems to require sooty black countershading for its expression, and reorganizes sootiness into vertical stripes instead of a more uniform sprinkling of hairs."
Seeing Spots: A variety of non-Appaloosa spots do occur in many breeds. Birdcatcher spots, named for the Thoroughbred stallion who exhibited them, are small white spots scattered throughout a horse's coat. In many cases, the spots appear and grow in number for a period of years, and then gradually fade away. Sometimes, the spots will persist throughout a horse's lifetime. Chubari spots are similar, but are usually larger, often egg-shaped and egg-sized. They seem to occur most frequently on grey coats, and of course, fade as the grey coat fades. Most grey TBs and grey horses with TB breeding can trace their spots back to The Tetrarch, a brilliant racehorse in England in the early 20th century. Bend Or spots are also named for the TB stallion who bore them. They are random dark spots on a lighter coat, often seen on chestnuts and palominos. They vary in size, sometimes only dime-sized, and sometimes as big as an outspread palm.