Basics
Before you try to grapple with understanding different genes and how they work and effect each other, you should first understand the basic terminology and how genes function.
In this example, we are testing the agouti (A) gene, where both parents have heterozygous genes. Agouti is a dominant gene, so it can express itself even if it is heterozygous.
- Allele - A single piece of a gene. The allele determines if the gene is active or not.
- Gene - A pair of alleles. Genes are characteristics that can be passed on to offspring, such as eye and hair color, behavior, and even diseases.
- Heterozygous - A gene that has one dominant allele and one recessive allele. (ex. Oo)
- Homozygous - A gene that's alleles are both dominant. (ex. OO)
- Dominant - An allele that expresses itself whether it is heterozygous or homozygous.
- Recessive - An allele that can only express itself if it is homozygous.
- Genotype - The genetic code, such as EE or OO.
- Phenotype - How a gene visually expresses itself, such as black or bay.
- Modifier Gene - A gene that can only work if certain genes are present.
In this example, we are testing the agouti (A) gene, where both parents have heterozygous genes. Agouti is a dominant gene, so it can express itself even if it is heterozygous.
The offspring produced by these parents would have a 50% chance to be heterozygous agouti, 25% chance to be homozygous agouti, and 25% chance to not have agouti at all. A foal produce by these parents would most likely be a bay horse, assuming that both parents are base black.
That is the most basic in genetics, and should help you as we get into the more complicated stuff.
That is the most basic in genetics, and should help you as we get into the more complicated stuff.
The Extension Gene (E)
All horse genes depend on one thing : is it red or black? There are a lot of horse genes, and countless combinations, but they are all built off of the extension gene; chestnut and black.
- Chestnut - The extension gene's recessive allele (e) produces pheomelanin, a red pigment.
- Black - The extension gene's dominant allele (E) produces eumelanin, black pigment.
Agouti (A, At, A+)
The agouti gene is a modifier, and will only show up if the horse is dominant black, and restricts black pigment to certain areas.
Unlike most other horse genes, agouti has a total of four alleles; a, A, At, and A+. Since there are different variations, agouti can't have a simple dominant recessive relationship, instead it has a sort of hierarchy.
Unlike most other horse genes, agouti has a total of four alleles; a, A, At, and A+. Since there are different variations, agouti can't have a simple dominant recessive relationship, instead it has a sort of hierarchy.
- The most recessive allele is a. Since agouti is a dominant gene, it must have two recessive alleles for agouti to not be present, which is why black horses are so rare.
- The second most recessive is At. At restricts black from a horse's soft points, making seal bay. Seal bay is also rare, since it is on the lower end of the hierarchy. To be seal bay, it must either have Ata or AtAt.
- Next is A, which creates the classic bay. A bay horse can be Aa, AA, or AAt.
- At the top of the hierarchy is A+. A+ makes a wild bay horse, and even though it is at the top, it is believed to be very rare. Since it is relatively new, information on wild bay isn't concrete. Wild bay, being the highest in the agouti hierarchy, will be present as long as there is at least one A+ allele present.
Grey (G)
Grey horses are not the same as a dominant white horse. Horses with the grey gene slowly start to grey out as they age, which causes dapple greys. Grey is a dominant gene and will overpower any other coloring the horse has.The easiest way to tell the difference between a white horse and a grey horse is the skin color; a white horse will be born white with pink skin and blue eyes, a grey horse will be born like any other horse with skin to match, and will become white over time.
The way grey behaves is vastly different from other genes; it doesn't always show up at birth. Horses grey out differently; some horses only take days after birth to show signs of grey, while others may take years. As a horse greys, it can create a variety of color patterns. There are two ending stages; white grey and fleabitten grey.
The way grey behaves is vastly different from other genes; it doesn't always show up at birth. Horses grey out differently; some horses only take days after birth to show signs of grey, while others may take years. As a horse greys, it can create a variety of color patterns. There are two ending stages; white grey and fleabitten grey.
- Dapple Grey : The median stage of greying, but not all horses go through a dapple grey stage. Can appear on any base color horse, but many consider it more attractive on a dark base horse.
- Rose Grey : Chestnut or bay horses that have grey hairs starting to show. This is sometimes confused with roan.
- Iron/Steel Grey : Similar to rose grey, only with a black or dark base horse.
- Mulberry Grey : A chestnut or bay base horse where the base coat shows through the grey. Mane and tail have dark roots and fade out towards the tips.
Cream (cr, prl)
Single cream dilutes can cause horses to be golden in color, such as palomino or buckskin. Cream affects the coat differently depending if it is heterozygous or homozygous. When it comes to cream, heterozygous cream genes are commonly called single dilutes, while homozygous cream genes are double dilutes. Single dilutes will lighten the coat, mane, and tail. Double dilutes (CRprl is a pseudo double dilute) will make the horse near white. The cream gene is unique in that it's not as easy to dilute black, which is why chestnut horses will be completely gold or cream, while bay horses' legs will remain black. However, a double dilute cream gene will overpower black hair. Double diluted horses will have pink skin and blue eyes.
More recently, another form of cream has been found ; pearl - also known as the ''Barlink factor''. Unlike most other genes, for pearl to show up, it must be recessive. A single allele of pearl by itself will do nothing to a horse's coat, but if it is paired with a dominant cream allele, it can make a pseudo double dilute. CRprl, in both chestnut and black horses, makes a "cream pearl" horse. Cream pearl is almost completely unnoticeable from double dilutes in that cream pearls have near white coats, pink skin, and blue eyes. Two pearl alleles will create a warm dilution.
More recently, another form of cream has been found ; pearl - also known as the ''Barlink factor''. Unlike most other genes, for pearl to show up, it must be recessive. A single allele of pearl by itself will do nothing to a horse's coat, but if it is paired with a dominant cream allele, it can make a pseudo double dilute. CRprl, in both chestnut and black horses, makes a "cream pearl" horse. Cream pearl is almost completely unnoticeable from double dilutes in that cream pearls have near white coats, pink skin, and blue eyes. Two pearl alleles will create a warm dilution.
Dun (D)
Dun horses are characterized by a lighter body color and 'primitive' markings. These markings retain the original body color.
The dun gene can affect all colors, and all horses with dun will have a dorsal stripe, and most have leg barring. Other markings include face masks, forehead spider webbing, shoulder and dorsal stripes (fishboning), and ear barring. The dorsal stripe is the dun factor, and is the easiest way to differentiate a dun horse from bay or buckskin. If the horse doesn't have a dorsal stripe, it's not a dun.
Dun is a very common color among wild horse breeds, and some breeds only consist of dun colors, such as przewalski, fjord, and konik horses.
DreamWorks' Spirit was a dunskin: buckskin + dun.
The dun gene can affect all colors, and all horses with dun will have a dorsal stripe, and most have leg barring. Other markings include face masks, forehead spider webbing, shoulder and dorsal stripes (fishboning), and ear barring. The dorsal stripe is the dun factor, and is the easiest way to differentiate a dun horse from bay or buckskin. If the horse doesn't have a dorsal stripe, it's not a dun.
Dun is a very common color among wild horse breeds, and some breeds only consist of dun colors, such as przewalski, fjord, and konik horses.
DreamWorks' Spirit was a dunskin: buckskin + dun.
Champagne (CH)
Champagne is an incredibly rare gene. It affects both red and black, and gives a horse freckled pink skin. Champagne horses have hazel or amber eyes.
Foals are born darker and have blue eyes. As they age their coat lightens out and their eyes turn hazel or amber. Sometimes dapples of the dark hair can be retained into adulthood.
Before the champagne gene was discovered, gold champagnes where sometimes called 'pumpkin-skinned palominos', and classic champagnes where called 'lilac duns'.
American Cream Drafts consist almost entirely of champagne colors. The foundation mare of this breed, Old Granny (~1905), was a gold champagne, and most ACDs owe their color consistency to the champagne gene. It wasn't until 1969 that the gene was discovered on a classic champagne Tennessee Walking Horse mare, Champagne Lady Diane. The owner sent hair samples to several universities, where it was written off as a "color accident". The champagne gene wasn't sequenced until 2008.
Foals are born darker and have blue eyes. As they age their coat lightens out and their eyes turn hazel or amber. Sometimes dapples of the dark hair can be retained into adulthood.
Before the champagne gene was discovered, gold champagnes where sometimes called 'pumpkin-skinned palominos', and classic champagnes where called 'lilac duns'.
American Cream Drafts consist almost entirely of champagne colors. The foundation mare of this breed, Old Granny (~1905), was a gold champagne, and most ACDs owe their color consistency to the champagne gene. It wasn't until 1969 that the gene was discovered on a classic champagne Tennessee Walking Horse mare, Champagne Lady Diane. The owner sent hair samples to several universities, where it was written off as a "color accident". The champagne gene wasn't sequenced until 2008.
Silver Dapple (Z) and Flaxen (F)
Silver dapple and flaxen are both categorized together because they both effect the mane and tail color of a horse.
Silver dapple will only show up on black base horses, and because it is a dominant gene, it will be present with only a single dominant allele. However, it is believe if silver is homozygous ZZ, the effect is stronger. Silver can sometimes spread past just the mane and tail and make a dappled appearance in the coat of the horse, hence the name 'silver dapple'. Usually horses with silver dapple will have a lighter coat pigment, black horses taking on a 'chocolate' color. Silver will not effect the look of a chestnut horse at all, so a chestnut horse may silently carry the gene.
Flaxen is the opposite of silver: it will only effect chestnut horses and it must be recessive to take effect. A horse with Ff or FF will not show flaxen. A black horse may silently carry the flaxen gene.
Silver dapple will only show up on black base horses, and because it is a dominant gene, it will be present with only a single dominant allele. However, it is believe if silver is homozygous ZZ, the effect is stronger. Silver can sometimes spread past just the mane and tail and make a dappled appearance in the coat of the horse, hence the name 'silver dapple'. Usually horses with silver dapple will have a lighter coat pigment, black horses taking on a 'chocolate' color. Silver will not effect the look of a chestnut horse at all, so a chestnut horse may silently carry the gene.
Flaxen is the opposite of silver: it will only effect chestnut horses and it must be recessive to take effect. A horse with Ff or FF will not show flaxen. A black horse may silently carry the flaxen gene.
Sooty (STY)
The sooty gene causes black hair to be mixed in with the coat. The black hairs are usually more obvious towards the top of the horse, along the spine. This can sometimes give the horse the appearance to have a dorsal stripe, and can sometimes effect the color of a horse's mane and tail. As the hairs grow in, they can make some interesting patterns, dappling and 'frosting' being the most common. Very rarely sooty can make a 'brindle' horse.
Rabicano (Rb)
Rabicano horses have white hairs intermingled in with the coat in certain areas. Usually this is the belly, flank, legs, and the edges of the tail. One of the main characteristics of a rabicano horse is what is called a 'skunk tail'.
Roan (rn+)
Roan is a KIT gene.
Horses with roan have white hairs throughout their body, with less roaning on the legs, head, mane, and tail. These white hair are distributed evenly, but spots of the base coat color can show throw if the hair is damaged in any way, as the white hairs will not grow back.
Horses with roan have white hairs throughout their body, with less roaning on the legs, head, mane, and tail. These white hair are distributed evenly, but spots of the base coat color can show throw if the hair is damaged in any way, as the white hairs will not grow back.
Sabino (sb1+)
Sabino is a KIT gene.
Sabino creates irregular marking on a horse's face, legs, and sometimes belly. The edges of these markings have an effect similar to roaning. When homozygous, a horse can be 90% white or more. Homozygous sabinos will have pink skin, but won't have blue eyes. Eye color can distinguish a homozygous sabino from a white or cremello horse.
Sabino creates irregular marking on a horse's face, legs, and sometimes belly. The edges of these markings have an effect similar to roaning. When homozygous, a horse can be 90% white or more. Homozygous sabinos will have pink skin, but won't have blue eyes. Eye color can distinguish a homozygous sabino from a white or cremello horse.
White (w+)
White is a KIT gene.
A truly white horse will have pink skin with blue or light colored eyes. Unlike grey horses, a true white will be white from birth. Homozygous white is lethal. Foals with homozygous white are aborted naturally by the mare early in gestation.
A truly white horse will have pink skin with blue or light colored eyes. Unlike grey horses, a true white will be white from birth. Homozygous white is lethal. Foals with homozygous white are aborted naturally by the mare early in gestation.
Tobiano (to+)
Tobiano is a KIT gene.
Tobiano horses have large, pink spots over it's base coat. Those pink spots make the hair white. Horses with tobiano will usually have dark skin on their head, chest, and flank, and will have white legs.
Tobiano horses have large, pink spots over it's base coat. Those pink spots make the hair white. Horses with tobiano will usually have dark skin on their head, chest, and flank, and will have white legs.
Overo (o)
An overo horse will have irregular white spots over it's base color, usually aligned horizontally. The lower legs usually are dark, while the head is white or bald faced. The mane and tail are usually not effected.
Overo is commonly called 'framed overo' because the base color 'frames' the markings from certain parts of the body, such as the back, buttock, belly, and legs.
Overo is commonly called 'framed overo' because the base color 'frames' the markings from certain parts of the body, such as the back, buttock, belly, and legs.
Splash (spl)
Splash is recorded as being in the overo family, but is separate from the overo gene. The reason for the name 'splash' or 'splash white' is because a horse with these gene will looked like it has been dipped in white paint. Splash horses will sometimes have blue eyes, even if the white coloring doesn't cross their eyes. The edges of splash markings are crisp and clean.
Heterozygous splash horses usually only have their legs effected, so it is harder to identify a heterozygous splash horse as such. Homozygous splash will make it look like the horse has been dipped in paint.
Heterozygous splash horses usually only have their legs effected, so it is harder to identify a heterozygous splash horse as such. Homozygous splash will make it look like the horse has been dipped in paint.
Varnish Roan (lp)
Also called "frost", varnish roan is the base gene required for any other appaloosa marking to show.
Varnish roan appaloosas have an uneven roaning pattern that increases with age. The speed at which the roaning increases varries from horse to horse. Usually a foal is born with some sort of spotting pattern, but the gradual roaning eventually overtakes this pattern. By adulthood, a horse will have more white hairs than dark hairs, dark hairs usually more dominant around the face and knees.
Varnish roan appaloosas have an uneven roaning pattern that increases with age. The speed at which the roaning increases varries from horse to horse. Usually a foal is born with some sort of spotting pattern, but the gradual roaning eventually overtakes this pattern. By adulthood, a horse will have more white hairs than dark hairs, dark hairs usually more dominant around the face and knees.
Leopard Appaloosa (patn1)
Leopard horses are so named for the leopard like markings that cover most of the horse.
PATN1 is a modifier gene, and requires varnish roan(lp) to be active to be visibly present.
PATN1 is a modifier gene, and requires varnish roan(lp) to be active to be visibly present.
- LPLP + PATN1_ makes a few spot appaloosa
- LPlp + PATN1_ makes a leopard appaloosa
Blanket Appaloosa (patn2)
Blanket appaloosa horses are named because of the fact that their markings look like someone threw a white blanket over them. Leopard is the dominant gene between the two patn genes. So even a horse with PATN1patn1 + PATN2PATN2 will be leopard. Like PATN1, PATN2 requires varnish roan(lp) to be active to be visibly present.
- LPLP + PATN2_ makes a snowcap appaloosa
- LPlp + PATN2_ makes a spotted blanket appaloosa