So You Want to Write about Horses: Color Edition
Well, your knight better not be riding in on a white horse, because that horse is actually grey! And what do you mean a brown horse? Is your cowboy's faithful horse sorrel or chestnut and what does it matter?
(Part 4! Enjoy this post? Want to know more? Check out So You Want To Write About Horses Part 1 and Part 2 and So You Want To Write About Horses: Medieval Edition)
Lets begin with base horse colors:
This is fairly easy. All horses are either red-based or black-based. The other colors of horses are all modifications on these two basic variations. A plain red-based horse is a chestnut horse. If you live West of the Mississippi river, you would call this horse a sorrel. Same thing.
A plain black-based horse is a black horse.
Genetically speaking, the choice between a black or a chestnut is controlled by the Extension gene, represented as E/e. A black horse is created when the genetics are either EE or Ee, as the Extension gene is dominant. A chestnut horse can only be ee, the regressive form with no black hair expression.
However, black horses are actually not that common, relatively speaking. Most horses are some form of chestnut, ee, or a bay.
The bay horse is a variation on a black base. They have black manes and tails, black on their legs, and red or brown bodies. A bay horse is created by the Agouti gene (A/a), which changes the expression of the Extension gene (E/e). So a horse with EE AA will be a bay horse, like above. A horse with Ee Aa will also be a bay horse, exactly the same. In order for a horse to be black, they must have a dominant Extension gene and a regressive Agouti gene, EE aa or Ee aa.
Chestnut horses have no black in their coat, so the Agouti gene cannot affect them. They can be carriers, however, and make a bay horse when paired with a black horse. A chestnut horse could be ee aa, ee Aa, or ee AA, and look completely the same.
Congradulations, you now know horse color genetics! Now for the fun ones.
If you've ever seen Spirit, Stallion of the Cimarron, you know this color
^This is the actual colt that Dreamworks animators modeled from!
Dun (D/nd1/nd2) is a gene that modifies all base coat colors. It can modify black, creating a black dun/grullo horse, it can modify bay, creating a bay dun, and it can modify chestnut, creating a red dun. In all of these variations, the body of the horse is lightened, the mane, tail, and legs are dark, and the horse has 'primitive' markings, including an eel stripe down the back, darker face, and leg bars.
If you notice, dun has three variations! D is the dominant form, so any horse with D is a dun of some kind. Nd1 is a variant in the same gene that gives the horse similar markings, but it is not dun, and will be over powered by the dominant D version. Nd2 is a horse with no dun factor, so no markings or lighter coat. Dun horses can be D/D, D/nd2, D/nd1. A horse with non-dun factor (and look similar to a dun) can be nd1/nd1 or nd1/nd2. A bay, black, or chestnut horse will be nd2/nd2.
Another gene diluting color is the cream gene, which you may know from the famous horse of Roy Rogers, Trigger
Trigger is a beautiful example of a palomino, a red-based cream dilute. As you can see, Trigger has a pale mane and tale and a gold colored body. Cream (Cr/Prl/-) is a dilution gene, or a hypomelanism gene, meaning it prevents red color in horse hair. Any red on a horse will be lightened. Chestnut horses, being all red, will have their entire bodies, mane, and tail lightened. Bay horses, with red hair only on their bodies, will have the body lightened, but the black mane, tail, and legs stay black, creating a buckskin horse
But wait! That horse looks exactly like the bay dun horse! Yes. Yes they do. However, buckskins do not have eel stripes, leg bars, or darker heads, and are a completely different gene. In fact, you can mix the two get a cream dun (Dunskin). It might be a slightly lighter dun.
Because a black horse has no red, black horses with the Cream dilute stay black, IF they have only one version (Ee aa Cr). Cream is an incomplete dominant gene, meaning that two versions makes the effect of the gene even stronger. Double creme dilutes are Cremellos, and they are very pale (but not white!)
The double creme dilute overrides all the other genes. They are still there, but the horse is so pale, you can't see them. A variation of this color is the perlino, a horse with a recessive dilute gene called Pearl (Prl/-)
Pearl is recessive, meaning that one copy does not change the horse's coat. Two copies creates the perlino, and because Pearl is on the same gene as Cream, a false cremello can be created by a horse with one cream gene and one pearl gene. Crazy, right?
Now, there are so many more genes, but lets skip ahead to some patterns.
These are technically not colors, but rather genes that selectively turn off color in certain areas to create a coat pattern in horses. The most important of these are Tobiano, Frame, and Appaloosa genes.
Tobiano is the gene for the coats of Paint horses (a color breed with a registry) and one of the genes for pinto horses. Pinto means any horse with large splashes of white, which includes the Frame gene, also known as Overo.
Both of these horses are Pintos, but only the lower one is an American Paint Horse, or Paint, and the top one has the Tobiano gene (TO), while the bottom has the Frame gene (O). A horse can be double Tobiano (TO/TO), Tobiano and Frame (known as Tovero) (TO/O), but a double Frame horse will die an early and painful death, due to Lethal White Factor.
Lethal White Overo is when two Frame horses are bred together and the foal receives the O gene from both parents. The foal can survive birth, but has malformations of the intestines that are incompatable with life. ALL affected horses die within days of birth.
Appaloosa horses are a very interesting horse. Technically, Appaloosa refers to a breed, developed by the Nez Perce tribe in the Pacific Northwest. Appaloosa is thought to come from "a Palouse horse", the name of a major river in the tribe's area. When the tribe was forced on a reservation, most of the horses were slaughtered or given to local white settlers, leading to many Appaloosa horses becoming merged to the Quarter Horse breed. As a result, most people use it as a color term.
Nancy Wak Wak (Umatilla) on an Appaloosa, 1937. Oregon Historical Society Research Library, 018041
The genes responsible for the Appaloosa pattern is the Leopard Complex, controlled by an incomplete dominant gene (Lp/-), which turns on the complex when present, and turns it off when absent. Several other genes control the amount of white, the type of white, how big the spots are, ect. One Lp turns the complex on, but two Lps creates a mostly white blanket, or a fewspot coat.
This horse has double Lp. The horse above it has one Lp, creating the many spotted coat.
Not all spotted horses are Appaloosas! In Denmark, the Knabstrupper is a breed of horse with no relation to the Appaloosa, but with the same gene creating the same spotted coat. Completely different breed, different origins, but same genes.
In all of these patterns, the pattern can be maximal, or very visible, or minimal, and not visible at all. A horse can look solid colored, but be hiding a pattern gene. So if you want to make babies, test your horse's genetics first! You do not want to accidentally cause a genetic deficiency.
Finally, the famous white horse.
Most 'white' horses are actually grey. White horses are very rare. Grey horses are called grey because they are born with a colored coat, but because of the Grey gene (G/g) they lose color as they get older. Grey horses go through many colors throughout their lives.
A grey foal and grey mother. Babies are born with the base color visible, but lose it as they age.
A dapple grey horse in the process of losing its baby coat.
A fully greyed-out horse at adulthood. Even all grey, the skin around it's eyes and nose is still black, because the skin underneath has not lost color, only the hair.
A white horse is born white, will always be white, and is never naturally any other color. The skin of a white horse is pink, because it, like the hair, does not have color.
Sodashi is a Japanese racehorse and a member of a super-rare white horse family. Several members of her family are pure white, due to a mutation that gives them extreme white pattern, much like with the Tobiano gene. Her relative, Buchiko, shows the minimal pattern that gives them their white color.
Same pattern, but maximal and minimal expression!
