Equine Coat Color Genetics

Lesson Three

The Cream Dilution

The term “dilute” is used to describe multiple colors: Cream, Champagne, Dun, Silver and Pearl…. Basically any one of the colors that result from a dilution of the pigment. These are all caused by different genes. With the exception of Pearl, they reside on different chromosomes. In this section, we will address the Cream dilution gene only.

A Quick Word About "Albino"

An albino is by definition “A person or animal lacking normal coloring in the eyes, hair, and skin due to a hereditary inability to produce the skin pigment melanin. The condition itself is called albinism.” (http://medical-dictionary.thefreedictionary.com/albino). Mice, rats and rabbits commonly carry this gene, which produces an all-white animal with red eyes (from the blood vessels showing through the clear, unpigmented iris) and pink skin, completely devoid of any color pigment. Studies have shown that the Equid species (all horses, mules, donkeys, asses, zebras, etc.) do not carry the genetic mechanism to produce an albino. Remember, “albino” in most animals denotes complete, total absence of color pigment. So a horse with a white coat, pink skin and blue eyes is not a true albino. This phenotype can be produced by any of several combinations of color-modifying genes. Most striking is that of a multi/maximum-pinto -- think of the horse being covered by so many white spots that there is no color left showing through anywhere -- produced by any number of pinto (aka spotting) genes. However, in the past, double Cream dilutes such as cremello, with a pale-cream-to-white coat, pink skin, and blue eyes, were commonly called “albinos”. They were even refused registration in some breeds because they were believed to be “defective”. All this has long since been proved false, of course. But it is something you may come across in older literature. The term “albino” is also used as a descriptive term by many people for any white animal. But as a genetically accurate term, it does not apply to horses.

The Cream gene

Cream is the most common of the dilution genes, giving the popular palomino and buckskin colors (among others). It has been known for many years, but was poorly understood in the early days. Cream is an incomplete dominant gene. Remember from Lesson 1, an incomplete dominant gene is one that has a different effect when heterozygous vs. when homozygous. Usually an incomplete dominant expresses itself in a stronger form when two copies are present (when homozygous).

As you will remember, the dominant allele uses an upper-case letter for the abbreviation, and lower-case is used for the recessive allele. In the case of a two-letter abbreviation such as this one (Cream is not the only gene that begins with the letter C, so “Cr” is for Cream and “Ch” is for Champagne) there is some disagreement about whether both should be upper-case, i.e. “CR”, or just the first letter, i.e. “Cr”. You will see it written both ways. Both ways mean the same thing. It’s somewhat easier to tell them apart at a glance if both are capitalized, but it seems more common to use “Cr” so that is what we will use.

So, the dominant Cream allele is: Cr. The recessive allele (which has no effect on the horse’s color) is: cr.

In the past (many years ago), the Cream gene was thought to be at the C locus. “C” is for “Color”, and is the albino locus in many animals. Even after it became understood that cremellos were not true albinos, it was still thought to be related, so it was theorized that Cream was an another allele at that locus. Rather than C or c, it was called cr. As we touched on in Lesson 1, in genetics it is common to use the gene locus abbreviation, with the allele abbreviation in superscript (this has been pretty universally dropped in horse color genetics since it’s redundant and confusing). So you may see the Cream gene called, in books that are very out of date, as “C^cr”. This is not genetically correct -- it has been known for many years that horses do not have this albino C locus. We only mention it so you will know what it means if you come across it.

The Cr mutation was isolated in 2001 (the official name given to the locus is MATP; you needn’t remember that) and a test has been available since 2003.

The Cream gene is the most widespread of the dilution genes and it is present in many breeds. It's common in all of the "Western" type American breeds such as Quarter Horse, Paint, Appaloosa, and Mustang. It's fairly common in most of the American gaited breeds such as the Saddlebred, Tennessee Walking Horse, Missouri Foxtrotter, and Racking Horse; and is present but not as common in Rocky Mountain and Mountain Pleasure horses. It's present but not common in the "Iberian" breeds such as the Paso Fino, Peruvian Paso, Andalusian, and Lusitano. It's present, but fairly rare, in the Morgan and Thoroughbred. It is present in a few Warmblood breeds like the Dutch, Danish, and Swedish Warmbloods, Oldenburgs, and possibly the Trakehner and Selle Francais. It is not present in the modern Standardbred or Hackney, or the Arabian; or (naturally) in breeds that have specified one color in the breed standard, i.e. the Friesian and Cleveland Bay. The only draft breed that is known to have the gene is the American Cream Draft (most of which are champagnes, but some are champagne creams). It occurs in several pony breeds such as Welsh, Shetland, Connemara, Icelandic, and Mini. Fjords are all dun, but some are cream as well. Haflingers, although often called "palomino", do not have the gene; they are all chestnut (some very light flaxen chestnut, but not palomino).

How it works

This gene is unique in its actions. When a horse has one copy (is heterozygous), it acts on any red hair by lightening it to golden yellow. Manes and tails are lightened even further, usually to white. The skin and eye color are not changed (although it's not uncommon for them to be born with pinkish skin and blue eyes, which darken to the normal adult color over a few days or weeks). Black hair is generally unchanged, although it often has a tendency to sunbleach much more readily, and some horses do seem to have more of a dark chocolate-brown tone than jet black. Any black "sooty" hairs that may be present will also remain undiluted, and this can be extreme. Eye color is not reliably affected by a single copy of the gene. Some of these horses do have lighter colored eyes, often called “amber” or “hazel” (though not really as light as those terms would suggest) but many do not, and some nondilute horses have similarly colored eyes.

When a horse has two copies of the gene (is homozygous), the effect is what is commonly called "double-diluted". Both red and black hair is diluted to a cream color, with the black hair usually having a slightly reddish or peachy tint. The skin is pink, and the eyes are light blue. If the horse has any white markings, they may or may not be visible. Some are so light they just "look white" all over. The pink skin under white markings ought to be a bit lighter -- technically speaking, the skin of a double-dilute does have some pigment, it is just diluted; while the skin under white markings has no pigment at all. For this reason the pink skin of a double-dilute does not tend to sunburn as readily as the pink skin under white markings. In practice, though, it can be very difficult to see any difference. The skin of double-dilutes does tend to develop some freckling over time, especially where exposed to the sun, but this is not to be confused with the freckling on a champagne; it looks quite different, not the darker, more distinct dots that champagne skin has, but a more subtle freckling like we might get on our skin. Blue eyes on a double dilute are not the result of a blue-eyed gene, but of dilution of the iris pigment, and when one breeds a double cream to a non-cream the resulting (single-dilute) foal will not have blue eyes (unless there are some other blue-eye-causing genes involved, unrelated to the Cream gene, of course).

Breeding for these colors

The incomplete dominant nature of this gene makes it a little tricky to breed for. Around 50-75 years ago the palomino color had a surge in popularity. They were favored as parade horses, there were famous movie and TV horses of that color, and there were two registries for Palominos in America which published stud books and magazines. The lack of genetic knowledge at the time led to some frustration for breeders when they found that palominos do not breed true. (Complicating this, however, was the fact that many of the “palominos” were in fact gold champagnes, which is an entirely different gene which does have the potential to breed true. But we will cover that gene later.) They bemoaned the “albinos” that would “pop up” without realizing that those cremellos were in fact the key to guaranteed palomino foals.

Breeding two palominos together would give you a 25% chance of chestnut, 50% chance of palomino, and 25% chance of cremello.

Punnett Square example:

	Cr	cr
Cr	Cr/Cr	Cr/cr
cr	Cr/cr	cr/cr

Breeding two single-Cream-dilutes (of any shade) together would give you the same 25% chance of nondilute, 50% chance of single dilute, and 25% chance of double dilute. But depending on the base colors involved, your chances of the various colors within each of those categories can vary greatly.

Now, if one were averse to double-dilutes, say you just don’t like the look, or don’t like trying to keep a “white” horse clean, or in the days when some registries would not accept them, then it would be wise to choose to breed only palomino x chestnut rather than palomino x palomino. You would have the same 50% chance of palomino but no chance of double-dilutes, so the other 50% would be chestnut.

Punnett Square example:

	Cr	cr
cr	Cr/cr	cr/cr
cr	Cr/cr	cr/cr

Now that we understand the heterozygous nature of the palomino color, there is a way to guarantee a palomino foal. Simply breed chestnut to cremello, and every foal will be palomino.

Punnett Square example:

	Cr	Cr
cr	Cr/cr	Cr/cr
cr	Cr/cr	Cr/cr

Again, this works with any double-dilute bred to any non-dilute. You are guaranteed a single-dilute foal. However the possibilities are greater depending on the base colors involved.

If one breeds a cremello to cremello one will always get a cremello. The effect of a double dose of the Cream gene is not magnified, and there is no increase in the full effect of the Cream gene in homozygous form. Each parent gives one Cream gene to the offspring insuring the resulting foal inherits two Cream genes. Remember, the maximum number of genes involved are two (homozygous state) and the genes will never “accumulate” when two double-dilute horses are bred together. This would seem to go without saying, but you may run across some “Old Wives Tales” from times past when people believed this sort of thing.

Palomino and Cremello

A chestnut with one Cream gene is called a palomino. The typical palomino is golden yellow with a white mane and tail. But like any other color, they range in shade from very light to very dark. A palomino can be so light as to appear near-white, or so dark as to appear near-black. The more extreme variations are rare, thank goodness! These can be difficult to identfy without genetic testing. The more common color range of light yellow to dark gold, almost coppery, is believed to be caused by the underlying base color, that is, whether the horse would have been a light chestnut, medium red chestnut, or dark liver chestnut, if it didn't have a Cream gene. This theory is logical, but unproven yet because it is unknown what genetic mechanism causes variations in shade. The really dark palominos are "sooty" and have black (or black-looking) hairs mixed into their body, mane and tail to varying degrees, even to the point of appearing nearly black all over.

A chestnut with two Cream genes is called a cremello. Typically they are a light cream color with white mane and tail. Usually they just look "white", especially from a distance. Some are dark enough to make out any white markings, some aren't. They sometimes get dapples, a subtle and beautful effect on this color. Like all double-dilutes, they have blue eyes and pink skin.

Typical Chestnut Typical Palomino Typical Cremello

It’s rather common for palominos to vary in shade with the seasons. Typically they are much lighter in winter coat, and darker in summer coat. Some have dapples year round, or never, but many are dappled in only one season or the other, or only while shedding.

Palomino in winter coat Same horse shedding out in spring Same horse in summer coat

Buckskin and Perlino

A bay with one Cream gene is called a buckskin. The single Cream gene changes the red body color of a bay horse to a golden or tan color, but does not affect the black points (mane, tail, ear tips, legs) of the horse. The typical buckskin is golden bodied with black points. Like palominos, they can range in shade from very light creamy yellow (often called "buttermilk buckskin") to a very dark gold (often called "bronze buckskin"). A buckskin that is "sooty" will have black hairs mixed in the coat, from a little to a lot. A very sooty buckskin can be so dark that it may not look dilute at all. Sooty buckskins are often strongly dappled.

Genetically speaking, the term “buckskin” has been used to cover anything with one Cream gene that is not “e/e” (or it would be palomino) or “a/a” (or it would be smoky). In other words, any kind of Agouti alleles other than both black; this would include the wild bay, regular bay, seal brown, and any yet undiscovered. The reason for this is twofold: one, they cannot be told apart visually, and two, the widely available test cannot tell them apart either (it only looks for the “a” allele). There is a test for the brown (“At”) allele now, but it’s only available from one lab and is a separate test from the regular Agouti test.

A bay with two copies of the Cream gene is called a perlino. Typically they are cream-colored on the body, with slightly darker, reddish-tinted points. Some are so light they look cremello, and some are darker, a pale peachy color all over. White markings are usually visible, but not always. Like cremellos, they can be so light that it is difficult to make out any white markings. Like all double-dilutes, they have blue eyes and pink skin.

Typical Bay Typical Buckskin Typical Perlino

Slightly sooty bay Slightly sooty buckskin

Extremely sooty bay Extremely sooty buckskin

Buckskins sometimes have what is called “frosting” which is a fringe of white hairs at the edges of the mane (and sometimes tail). It’s more common on young horses, and they often outgrow it, though not always. This occurs because some bays have some red hair along the edge of the mane, and the Cream gene turns red manes/tails to white.

Frosting on manes

Buckskins can change shades with the seasons too, like palominos. The following pictures are the same three horses in winter and summer coats:

Brown Buckskin and Brown Cream

A seal brown with one Cream gene is generally called brown buckskin. They may look like a dark, sooty buckskin, or they may look like a seal brown with little or no clue that the dilution is present. Only genetic testing can tell them for certain apart from a dark buckskin or a seal brown. (Remember, a single Cream gene has little or no effect on black hair, and seal browns are mostly black.) Unless they have been tested and proved to be seal brown based genetically, they are just called dark buckskin.

There is no “official” name for this color because registries don't have a separate category for them, so they are usually registered as brown, if dark, or as buckskin, if light enough to appear diluted. Most people call it brown buckskin or brown-based buckskin, although there has been talk of giving them a name (“brownskin” and “brunskin” have been proposed) it never has caught on. You may see them called two more names which are visually descriptive but not genetically correct: “black buckskin” and “smoky brown”.

A seal brown with two copies of the Cream gene is called brown cream, or sometimes brown double cream, and looks like a perlino or smoky cream. It is not possible to tell them apart just by appearance; genetic testing to determine the base color is needed (unless the parents’ genetics are known and only one result is possible). They would typically be registered as perlino, if that is an option. We do not have a photo of a verified brown cream at this time.

Typical Seal Brown Brown Buckskin (darker shade) Brown Buckskin (lighter shade)

Smoky Black and Smoky Cream

A black with one Cream gene is called smoky black, or just smoky. Often they don't look any different from a regular black, but some look almost like a liver chestnut, seal brown, or grulla. It's not uncommon for them to bleach out in the summer to a buckskin or grulla-like shade. At birth they often, but not always, have pinkish skin, blue eyes, and golden hair inside the ears; these can be good clues that a foal is a smoky, but only testing can say for sure. Most registries do not recognize the color, so they are typically registered as black, brown, or grulla.

A black with two Cream genes is called smoky cream. Theoretically, they should be a bit darker in shade than a perlino, but in real life these have been found in a variety of shades from light like a cremello, to a darker peachy cream, to almost a light greyish tone. Genetic testing is usually needed to pinpoint exactly what color they are. Registries typically don't recognize smoky creams and would call them perlino, if that color is recognized, or whatever else they felt was closest.

Black Smoky Black Smoky Cream

More smoky black examples of various shades

On the left is a brown buckskin; on the right a smoky black; they are sun-bleached in late summer and look buckskin.

Foal colors

Usually it is obvious what color a single-cream-dilute foal is at birth, but not always. Some are born a much darker shade than they will end up. It’s common for them to have pink-or-pinkish skin and blue-or-bluish eyes at birth, but this is not a guarantee, as some nondilute foals have had pinkish skin and bluish eyes at birth (especially chestnuts). In the days before the test, we just had to watch and see how the color changed over the next few weeks or months. Now, if we get impatient, we can pull some hair, mail it off, and have the answer in a few days. Double-dilutes are very hard to tell apart at birth (and often later on as well). Dorsal stripes are not uncommon on buckskins and smoky blacks; this is the cause of plenty of confusion in the past, but is not related to the Dun gene – dorsal stripes can occur on any color foal. Buckskin foals, like bay foals, typically do not have black legs at first, but some do. The most drastic change comes from the brown buckskin foals; just as a seal brown foal is typically born looking like a bay and then sheds out dark, the same thing happens with a brown buckskin.

Palomino foal, newborn, almost chestnut looking The same foal 2 days old The same foal 2 months old

Cremello foal, dark enough to see markings Cremello foal, looks white

Buckskin foal, almost as dark as a bay foal More typical buckskin foal color Buckskin newborn with blacker legs than most

Typical smoky black foal color Smoky black a few months old, coat faded, showing dorsal stripe

Brown buckskin foals – newborn color

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