By Loretta P. Brown, MS, MD
Reprinted from "The Palomino Parade"newsletter
What is a Palomino? A Palomino is a chestnut horse with a single dose of the Palomino dilution gene "cr." There are basically only two colors of horses: black and chestnut. All other colors are modifications of these by numerous genes present in the horse which influence the final color we see.
Two terms must be defined: genetype and phenotype. The genetype of a horse is the actual genetic make-up of the individual. The phenotype is what we can see outwardly ~ i.e. color· Each individual has two genes for each trait: one from each parent. These genes are represented by letters to allow us to work with them and to predict the likely outcomes of particular matings· The gene for black is represented by the letter "B," the gene for chestnut by "b." Black is dominant to chestnut and will be expressed over chestnut. The genetype of a black horse can be expressed as BB or Bb. We cannot tell by looking at a black horse whether it is BB or Bb. However, we can find out by looking at the color of the parents or offspring. If one of the parents of a black horse was a chestnut, then the black horse must be Bb. This "hybrid" black horse will be able to pass on the chestnut gene "b," but 50% of the time. If it is mated to another horse carrying the chestnut gene, a chestnut foal can be produced.
A chestnut must breed true by definition, since it is recessive. A chestnut horse's genetype is bb. WHEN TWO CHESTNUT HORSES ARE MATED, ALL FOALS WILL BE CHESTNUT. (Mutations can occur, but this only happens about one in a million times.)
There is another gene which modifies the black horse to brown or bay, and gives the different shades of chestnut· This is the "A" gene. Whereas the "B" gene had only two different forms or alleles ("B" and "b"), the "A" gene has three alleles: "A", "at" and "a." "at" is dominant to "a", and "a" is recessive to both. "A" is the bay gene, "at" is the brown gene and "a" is the black gene. The "a" gene allows the basic color, black to show through. The other two genes modify the black to bay or brown. The same modifiers give us the different shades of chestnut·
Now, finally, to the Palomino gene. This is a color dilution gene which dilutes the color of a chestnut to Palomino, and that of a bay to buckskin. The normal or undiluted form of the gene is represented by the letter "C". The dilution by the letters "cr". The Palomino dilution gene, "cr" is not expressed in a black or brown horse and can remain hidden for generations. It is possible to cross two black horses and get a Palomino foal! A chestnut horse, bb with one dose of the Palomino dilution gene, will be Palomino. If it has two doses of the Palomino dilution gene, one from each parent, it will be a cremelie in color. A cremelie is a very light horse: almost white in color. However, a true cremelie when crossed to a chestnut horse will give a Palomino foal 100% of the time (barring mutations of course).
By definition, then a Palomino is a hyrid. It carries only one dose of the Palomino dilution gene. Because it is a hybrid, it cannot breed true. When two Palominos are crossed to one another, there is a 50% chance of getting a Palomino, a 25% chance of a chestnut and a 25% chance of getting a cremelie. There are NO alibinos produced. The very light horses with blue eyes are cremelies.
So now we know a Palomino is genetically represented by "bb Ccr": chestnut and one dose of the Palomino dilution gene.. · what about the different shades of Palomino? This is where the "A" gene comes in. This gene which gave the different shades0f chestnut is also responsible for the different shades of Palomino. If one wants to darken the color of a Palomino parent, it should be bred to a darker chestnut. Conversely, if one wishes to lighten the color, breed to a lighter chestnut. The color is determined by the genes which can be passed on equally by sire or dam. If a horse, stallion or mare is a Palomino, it will pass that gene on 50% of the time. Remember, however that it is a game of chance ·. just like flipping a coin. Sometimes heads seem to come up most of the time. But if you throw that coin often enough, the overall ration will be 50-50.
We have learned that a Palomino is produced by the action of single Palomino dilution gene, "cr" in an otherwise genetically chestnut horse. A double dose of this Palomino dilution gene in a chestnut will produce cremelie. A bay with one Palomino dilution gene becomes a buckskin and a double dose of the dilution gene, becomes a perline (white hair, pink skin, blue eyes).
Now, just when you feel that you understand it all, along comes ANOTHER dilution gene. This gene is called the "D" gene and is expessed in any color horse. This is in contrast to the Palomino dilution gene which is not expressed in black or brown horses.
"D" is called the dominant dilution gene. In a black er brown horse, this "D" gene give a color known as grulla. This can range from a slate grey to a muted light brown or mouse color depending on the basic shade of the black or the brown horse in which it appears: i.e. lighter brown horses will be diluted to lighter colors. This "D" gene in a chestnut horse gives a dun: the body is a diluted shade of chestnut, the legs are a darker shade of chestnut and the mane and tail are also a shade of chestnut. These duns usually have a dorsal stripe. IMPORTANT: The "D" gene will NOT produce a Palomino.
This becomes even more confusing if we realize that the "D" dilution gene is thought to produce a color known as Isabella: a yellow body with a pale (but not white) mane and tail. It may be very difficult to tell these Isabellas from light Palominos! Again the use of Isabellas will prevent you from producing the ideal Palomino with its beautiful gold body and pure white mane and tail.
These subtle differences are not important for showing or enjoying your horses. They are, however of paramount importance if your goal is to BREED the ideal Palomino and to have a breeding herd which will give you a good chance of doing so again and again. Because of this, a word of caution to breeders. I would not recommend the use of breeding horses which have the "D" dilution gene in their pedigree. That is, horses with grulla or dun in their immediate ancestors or offspring. I am sure there will be folks who have such horses who have produced Palomino, but is that because they also carry the Palomino gene in addition to the "D" gene? However, if horses with the "D" gene are used in a breeding program, they will decrease the predictability of the offspring, as well as the chances of producing the ideal Palomino.
"My Palomino has only one line of gold horses in its pedigree: it is not very strong in Palomino." "My chestnut has 20 Palomino ancestors. I will surely get a Palomino when I breed it." "My Palomino has so many gold horses in its pedigree." "It is much more likely to produce a Palomino than if it only had a single Palomino line."
These are common conceptions about the importance of pedigree in the breeding of Palominos. And they are TOTALLY INCORRECT if we are solely interested in producing a Palomino colored horse. The Palomino with many gold horses in its pedigree is no more likely to produce a Palomino foal than the horse with only a single gold line. And the chestnut horse with many Palomino ancestors will never have a Palomino foal unless it is bred to a horse which carries a Palomino gene. The reasons for this should be clearer if one reviews the earlier explanation on the genetics of Palomino. Every Palomino horse carries a Palomino gene and has the same chance of passing it on to its offspring. It does not matter how many Palominos are in its background. Conversely, the chestnut horse does NOT carry a Palomino gene and; therefore, cannot pass it on.
So why bother looking at horses' pedigrees? Surely not if you only wish to produce a Palomino foal: ANY Palomino foal. Breeders do a disservice to the Palomino color when they breed for color alone. One must look at the quality of the animal produced. That is where the importance of pedigree comes in.
If breeders continue to breed for color alone, some ugly and unsound horses will be produced. No one wants an ugly horse: and an unsound horse, regardless of its color, is a waste. One must breed good horses to good horses. First and foremost, your Palomino must be a good horse. Then one can add the color. The pedigree is important in deciding whom to breed to whom on the basis of breeding sound horses first. ANY Palomino can pass on its Palomino gene. But placing that gene in a beautiful and correct animal is the trick.
So primarily, the pedigree is important to produce GOOD animals. Than the pedigree becomes important in breeding for the quality of color. Here again the number of Palominos in the pedigree is not as important as the quality of the color. Once you have a good horse, then improve the color. Breed out smut. Breed out dark hairs in mane and tails. Then breed the depth of color which you prefer: be it light, medium or dark. But breed for purity of color, not just for the presence of color. This is where the pedigree comes in. It may be difficult because most of the time one cannot know the quality of the Palomino color in the ancestors. If one can find a breeder who has information on the quality of the color of the horses in the pedigree, it can be of great help. Also knowing the shade of the chestnut horses involved also helps. Remember to darken the Palomino color breed to a darker chestnut and visa versa. Look for the purity of the whiteness of the manes and tail in the ancestors. This is very important since it is easier to lighten or darken the coat shade than to rid oneself of dark manes and tails.
Remember, do not breed to a horse which carries the Palomino gene just because it carries this gene. Breed to the horse because it is a good horse. Imagine this horse without its Palomino color. What do you think of the horse now? Do you still like it? If the answer is yes, then go ahead and breed it. You may be lucky and get the Palomino gene, AND a nice horse. The same holds true for a mare. Do not breed her if you would not breed her if she were a different color. To improve the Palomino, everyone must be willing to try and produce only good horses first, than make them beautiful with the Palomino color.