The
cream gene is responsible for a number of
horseThe horse is a hoofed mammal, a subspecies of one of seven extant species of the family Equidae. The horse has evolved over the past 45 to 55 million years from a small multi-toed creature into the large, single-toed animal of today...
coat colorsHorses exhibit a diverse array of coat colors and distinctive markings. A specialized vocabulary has evolved to describe them. Color is one of the first things that is noticed about a horse...
. Horses that have the cream gene in addition to a base coat color that is
chestnutChestnut is a hair coat color of horses consisting of a reddish-to-brown coat with a mane and tail the same or lighter in color than the coat. Genetically and visually, chestnut is characterized by the absolute absence of true black hairs...
will become
palominoPalomino is a coat color in horses, consisting of a gold coat and white mane and tail. Genetically, the palomino color is created by a single allele of a dilution gene called the cream gene working on a red base coat...
if they are heterozygous, having one copy of the cream gene, or cremello, if they are homozygous. Similarly, horses with a bay base coat and the cream gene will be buckskin or perlino. A black base coat with the cream gene becomes the not-always-recognized
smoky blackSmoky black is a hair coat color of horses in which the coat is black or a few shades off true black. Smoky black is produced by the action of a heterozygous cream gene on an underlying black coat color...
or a smoky cream.
Cream horses, even those with blue eyes, are not
whiteWhite horses are born white and stay white throughout their life. White horses may have brown, blue, or hazel eyes. "True white" horses, especially those that carry one of the dominant white genes, are rare...
horses. Dilution coloring is also not related to any of the
white spotting-General:*Conspiracy of the Pintos, a rebellion against Portuguese rule in Goa, India in 1787*Ford Pinto , a subcompact car manufactured by the Ford Motor Company for the North American market...
patterns.
The cream gene (
CCr) is an
incomplete dominantIn genetics, dominance describes a relationship between different forms of a gene at a particular physical location on a chromosome. Typical plants and animals have two sets of chromosomes, one set inherited from each parent, and are described as diploid. They therefore have two alleles at each...
allele with a distinct dosage effect. The
DNADeoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms and some viruses. The main role of DNA molecules is the long-term storage of information...
sequence responsible for the cream colors is the cream
alleleAn allele is one of a series of different forms of a gene. The word is a short form of allelomorph , which was used in the early days of genetics to describe variant forms of a gene detected as different phenotypes...
, which is at a specific
locusIn the fields of genetics and evolutionary computation, a locus is the specific location of a gene or DNA sequence on a chromosome. A variant of the DNA sequence at a given locus is called an allele. The ordered list of loci known for a particular genome is called a genetic map...
on the
MATPMembrane-associated transporter protein is a protein that in humans is encoded by the SLC45A2 gene.-Further reading:...
gene. Its general effect is to lighten the coat, skin and eye colors. When one copy of the allele is present, it dilutes "red" pigment to yellow or gold, with a stronger effect on the
maneThe mane is the hair that grows from the top of the neck of a horse or other equine, reaching from the poll to the withers, and includes the forelock or foretop. It is thicker and coarser than the rest of the horse's coat, and naturally grows to roughly cover the neck...
and tail, but does not dilute black color to any significant degree. When two copies of the allele are present, both red and black pigments are affected; red hairs still become cream, and black hairs become reddish. A single copy of the allele has minimal impact on eye color, but when two copies are present, a horse will be blue-eyed in addition to a light coat color.
The cream gene is one of several of hypomelanism or
dilution geneDilution gene is a popular term for any one of a number of genes that act to create a lighter coat color in living creatures. There are many examples of such genes:-General:...
s identified in
horseThe horse is a hoofed mammal, a subspecies of one of seven extant species of the family Equidae. The horse has evolved over the past 45 to 55 million years from a small multi-toed creature into the large, single-toed animal of today...
s. Therefore, is not always possible to tell by color alone whether the
CCr alleleAn allele is one of a series of different forms of a gene. The word is a short form of allelomorph , which was used in the early days of genetics to describe variant forms of a gene detected as different phenotypes...
is present without a DNA test. Other dilution genes that may mimic some of the effects of the cream gene in either single or double copies include the
pearl geneThe Pearl gene, also known as the "Barlink factor," is a dilution gene that somewhat resembles the cream gene and the champagne gene, but is neither. It is a somewhat rare dilution gene found in the American Quarter Horse, American Paint Horse, and Peruvian Paso. The same mutation appears in...
,
silver dapple geneThe silver dapple gene is a dilution gene that affects the black base coat color. It will typically dilute a black mane and tail to flaxen, and a black body to a shade of brown or chocolate. It is responsible for a group of coat colors in horses called "silver dapple" in the west, or "taffy" in...
, and the
champagne geneThe champagne gene is a simple dominant allele responsible for a number of rare horse coat colors. The most distinctive traits of horses with the champagne gene are the hazel eyes and pinkish, freckled skin, which are bright blue and bright pink at birth, respectively...
. Horses with the
dun geneThe dun gene is a dilution gene that affects both red and black pigments in the coat color of a horse. The dun gene has the ability to affect the appearance of all black, bay, or chestnut -based horses to some degree by lightening the base body coat and suppressing the underlying base color to the...
also may mimic a single copy of the cream gene. To complicate matters further, it is possible for a horse to carry more than one type of dilution gene, sometimes giving rise to coloring that researchers call a
pseudo double dilute.
The discovery of the cream gene had a significant affect on breeding, allowing homozygous blue-eyed creams to be recognized by many breed registries that had previously registered palominos but banned cremellos, under the mistaken notion that homozygous cream was a form of
AlbinismAlbinism is a form of hypopigmentary congenital disorder, characterized by a partial or total lack of melanin pigment in the eyes, skin and hair, or more rarely...
.
Colors produced
Cream coat colors are described by their relationship to the three "base" coat colors:
chestnutChestnut is a hair coat color of horses consisting of a reddish-to-brown coat with a mane and tail the same or lighter in color than the coat. Genetically and visually, chestnut is characterized by the absolute absence of true black hairs...
, bay, and
blackBlack is a hair coat color of horses in which the entire hair coat is black. Black is a relatively uncommon coat color, and novices frequently mistake dark chestnuts or bays for black. However, some breeds of horses, such as the Friesian horse, Murgese and Ariegeois are almost exclusively black...
. All horses obtain two copies of the MATP gene; one from the sire, and one from the dam. A horse may have the cream allele or the non-cream allele on each gene. Those with two non-cream alleles will not exhibit true cream traits. Horses with one cream allele and one non-cream allele, popularly called "single dilutes," exhibit specific traits: all red pigment in the coat is gold, while the black pigment is either unaffected or only subtly affected. These horses are usually palomino, buckskin, or smoky black. These horses often have light brown eyes. Horses with 2 copies of the cream allele also exhibit specific traits: cream-colored coats, pale blue eyes, and rosy-pink skin. These horses are usually called cremello, perlino, or smoky cream.
Heterozygous creams ("single dilutes")
Horses that are heterozygous creams, that is, have only one copy of the cream gene, have a lightened hair coat. The precise cream dilute coat color produced depends on the underlying base coat color. Unless also affected by other, unrelated genes, they maintain dark skin and brown eyes, though some heterozygous dilutes may be born with pink skin that darkens with age. Some have slightly lighter, amber eyes. However, the heterozygous cream dilute (CR) must not be confused with a horse carrying
champagne dilutionThe champagne gene is a simple dominant allele responsible for a number of rare horse coat colors. The most distinctive traits of horses with the champagne gene are the hazel eyes and pinkish, freckled skin, which are bright blue and bright pink at birth, respectively...
. Champagne (CH) dilutes are born with pumpkin-pink skin and blue eyes, which darken within days to amber, green or light brown, and their skin acquires a darker mottled complexion around the eyes, muzzle, and genitalia as the animal matures. It is also possible for a heterozygous cream horse to carry more than one of the other dilution alleles. (
see "Cream mimics,"
below) In such cases, they may exhibit some characteristics more typical of a homozygous dilute.
PalominoPalomino is a coat color in horses, consisting of a gold coat and white mane and tail. Genetically, the palomino color is created by a single allele of a dilution gene called the cream gene working on a red base coat...
is the best known cream-based coat color, and is produced by the action of one cream allele on a chestnut coat. It is characterized by a cream or white mane and tail and yellow or gold coat. The classic golden shade akin to that of a newly-minted gold coin is common, but there are other variations: the darkest shades are called sooty palominos, unusual but most often seen in
MorgansThe Morgan is one of the earliest horse breeds developed in the United States. Tracing back to the stallion Figure, later named Justin Morgan after his best-known owner, the breed excels in many disciplines, and is known for its versatility....
, can include a mane and tail with darker hairs and heavy dappling in the coat. The palest varieties can be nearly white, retaining darker skin and eyes, are sometimes mistakenly confused with cremello, and are called
isabellasIsabelline is a colour, sometimes described as pale grey-yellow, pale fawn, pale cream-brown or parchment.With horses, Isabelline or Isabella Palomino are terms applied to very pale palomino horses whose coat colour is cream, pale yellow or almost white. It is sometimes also applied to cremellos...
in some places.
Buckskin is also a well-known color, produced by the action of one cream gene on a bay coat. All red hairs in the base coat are diluted to gold. The black areas, such as the mane, tail and legs, are generally unaffected. The cream gene acting on a "blood bay" coat, the reddest shade, are pale gold with black points. They are sometimes called
buttermilk buckskins. The cream gene acting on the darkest bays, (sometimes mistaken for seal browns) may dilute to a
sooty buckskin. True
seal brownSeal brown is a hair coat color of horses characterized by a near-black body color, with a black mane, tail and legs, and reddish or tan areas around the eyes, muzzle, behind the elbow and in front of the stifle...
buckskins can be very difficult to identify owing to their almost all-black coats. It is only the reddish markings around the eyes, muzzle, elbow and groin, which are turned gold, that may give them away.
Smoky blackSmoky black is a hair coat color of horses in which the coat is black or a few shades off true black. Smoky black is produced by the action of a heterozygous cream gene on an underlying black coat color...
, a horse with a black base coat and one copy of the cream allele, is less well-known than the two golden shades. Since a single copy of the cream gene primarily affects red pigment, with only a subtle effect on black, smoky blacks can be quite difficult to identify. Smoky blacks may have reddish guard hairs inside their ears, and experienced horse persons may detect something "off" about the coat of a smoky black, though the slightly burnished look is often chalked up to sun bleaching, which can also be seen in true blacks. The palest can be mistaken for bays or liver chestnuts, especially if exposed to the elements. Smoky black coats tend to react strongly to sun and sweat, and many smoky blacks turn a chocolate color with particularly reddish manes and tails. Bleaching due to the elements means that the legs retain their color better, and can take on an appearance of having dark points like a bay horse. Smoky blacks, however, will lack rich red tones in the coat, instead favoring chocolate and orange tones. Because smoky blacks are often not recognized as such, breeders sometimes think that the cream gene "skipped" generations.
While there are "
color breedA color breed is a term that refers to horses that are registered based primarily on their coat color, regardless of the horse's actual breed or breed type....
" registries for palomino and buckskin horses, which generally record horses based on apparent
phenotypeA phenotype is any observable characteristic or trait of an organism: such as its morphology, development, biochemical or physiological properties, or behavior. Phenotypes result from the expression of an organism's genes as well as the influence of environmental factors and possible interactions...
and do not require a DNA color test, it is impossible for these colors to breed "true" due to the action of a single copy of the cream allele. Crossing two heterozygous dilutes will statistically result in offspring which are 25% the base color, 25% homozygous dilute, and 50% heterozygous dilute.
Homozygous creams ("double dilutes")
When a horse is homozygous, meaning it has two copies of the cream allele, the strongest color dilution occurs.
- "Cremellos are Homozygous cream chestnuts, and have a cream colored body with a cream or white mane and tail.
- Perlinos are Homozygous cream bays, which also have a cream-colored body but a mane and tail that may be somewhat more reddish in color than a cremello. *Smoky Creams are Homozygous cream blacks, and very difficult to visually distinguish from cremellos or perlinos.
All three shades can be difficult to distinguish from one another, and are oftentimes only firmly identified after a DNA test. While both red and black pigments are turned cream, the black pigment retains a little more color and tends to have a reddish or rusty tint. Thus all-red coats are turned all-ivory, all-black coats are turned all-rusty cream, and bay coats have ivory bodies with slightly darker points.
Horses with two copies of the cream allele can be collectively called double-dilutes, homozygous creams, or blue-eyed creams, and they share a number of characteristics. The eyes are pale blue, paler than the unpigmented blue eyes associated with white color or white
markingsMarkings on horses usually are distinctive white areas on an otherwise dark base coat color. Most horses have some markings, and they help to identify the horse as a unique individual. Markings are present at birth and do not change over the course of the horse's life...
, and the skin is rosy-pink. The true, unpigmented pink skin associated with white markings is clearly visible against the rosy-pink skin of a double-dilute, especially when their coat is wetted down. The palest shades of double-dilute coats are just off-white, while the darkest are distinctly rust-tinged. Their coats may be described as nearly white or ivory in addition to cream.
The off-white coat, pale blue eyes, and rosy pink skin distinguish the coats of double-dilutes from those of true
white horsesWhite horses are born white and stay white throughout their life. White horses may have brown, blue, or hazel eyes. "True white" horses, especially those that carry one of the dominant white genes, are rare...
. True white horses have unpigmented skin and hair due to the incomplete migration of melanocytes from the neural crest during development.
No health defects are associated with the cream gene. This is also true of the normal variations in skin, hair and eye color encoded on the human MATP gene. True white coat coloring can be produced by at least half a dozen known genes, and some are associated with health defects. Some genes which encode a white or near-white coat when heterozygous, popularly called "dominant white," may be lethal in homozygote embryos. Another specific mutation on the
Endothelin receptor type BEndothelin receptor type B, also known as ETB, is a human protein.Endothelin receptor type B is a G protein-coupled receptor which activates a phosphatidylinoitol-calcium second messenger system. Its ligand, endothelin, consists of a family of three potent vasoactive peptides:...
(EDNRB) gene is associated with the
frame overoOvero refers to several genetically-unrelated pinto coloration pattern of white over dark body markings in horses. Overo is a Spanish word, originally meaning “like an egg."There are at least three genetically different different spotting patterns which fall under the "overo" classification: frame...
pattern produces
Lethal white syndromeLethal White Syndrome , also called Overo Lethal White Syndrome , Lethal White Overo , and Overo Lethal White Foal Syndrome , is an autosomal genetic disorder most prevalent in the American Paint Horse. Affected foals are born after the full 11-month gestation and externally appear normal, though...
if homozygous, but carriers can be identified with a DNA test.
Prevalence
The cream gene is found in many breeds. It is common in American breeds including the
American Quarter HorseThe American Quarter Horse is an American breed of horse that excels at sprinting short distances. Its name came from its ability to outdistance other breeds of horses in races of a quarter mile or less, where some individuals have been clocked at speeds up to 55 mph...
,
MorganThe Morgan is one of the earliest horse breeds developed in the United States. Tracing back to the stallion Figure, later named Justin Morgan after his best-known owner, the breed excels in many disciplines, and is known for its versatility....
,
American SaddlebredThe American Saddlebred, formerly known as the American Saddle Horse, is a breed of horse that was developed in Kentucky by plantation owners. Today, in the horse show world, they are most commonly seen under saddle in Saddle seat style riding, and in various types of driving, including pleasure...
, Tennessee Walking Horse, and
Missouri Fox TrotterThe Missouri Fox Trotter is an American breed of horse with a unique four beat gait. It was bred in the Ozark Mountain foothills, and used by settlers who valued its smoothness.-Breed characteristics:...
. It is also seen in the
Miniature horseMiniature horses are found in many nations, particularly in Europe and the Americas. The designation of miniature horse is determined by the height of the animal, which, depending on the particular breed registry involved, is usually less than as measured at the last hairs of the mane, which are...
,
Akhal-TekeThe Akhal-Teke, 'Ahalteke' in the Turkmen language, is a breed of horse from Turkmenistan, where they are a national emblem. They are noted for their speed and for endurance on long marches. These "golden-horses" are adapted to severe climatic conditions and are thought to be one of the oldest...
,
Icelandic horseThe Icelandic horse is a breed of horse developed in Iceland. Although the horses are small, at times pony-sized, most registries for the Icelandic refer to it as a horse. Icelandic horses are late-developers, but are also long-lived and hardy...
,
Connemara ponyThe Connemara pony is a pony breed originating in Ireland. They are known for their athleticism, versatility and good disposition. The breed makes excellent show ponies.-History:...
, and
Welsh ponyThe Welsh Pony is a breed of pony that originated in Wales in the United Kingdom. The breed registries for the Welsh pony has four sections, primarily distinguished by height, but also by minor variations in type: the Welsh mountain pony , the Welsh pony , the Welsh pony of cob type , and the...
. It is even found in certain lines of
ThoroughbredThe Thoroughbred is a horse breed best known for its use in horse racing. Although the word "thoroughbred" is sometimes used to refer to any breed of purebred horse, it technically refers only to the Thoroughbred breed...
s,
WarmbloodWarmbloods are a group of middle-weight horse types and breeds, primarily originating in Europe, registered with organizations that are characterized by open studbook policy, studbook selection, and the aim of breeding for equestrian sport...
s, and the
Lusitanoj:For the Portuguese music theorist, please see Vicente Lusitano.The Lusitano is an ancient Portuguese horse breed, that until the 1960s shared its registration with the Spanish Andalusian horse. Both are sometimes called Iberian horses, as they originated from the Iberian peninsula. They were...
. The
Andalusian horseThe Andalusian, also known as the Purebred Spanish Horse or PRE , is a horse breed from the Iberian Peninsula. It is extremely similar to the closely related Lusitano breed. There are several competing registries that cover the Andalusian/PRE breed...
has conflicting standards, with the cream gene being recognized by some registries, but not explicitly mentioned by others. The cream gene is completely absent from the
Arabian horseThe Arabian or Arab horse is a breed of horse that originated in the Middle East. With a distinctive head shape and high tail carriage, the Arabian is one of the most easily recognizable horse breeds in the world. It is one of the oldest horse breeds, with archaeological evidence of horses that...
genepool, and is also not found in breeds with stringent color requirements, such as the
Friesian horseThe Friesian is a horse breed originating in Friesland, a province of the Netherlands. Although the breed's conformation resembles that of a light draft horse, Friesians are graceful and nimble for their size. During the Middle Ages, it is believed that the ancestors of Friesian horses were in...
.
Cream mimics
Other coat colors may mimic the appearance of a cream coat color. The presence or absence of the cream gene can always been verified by the use of a DNA test. Also, as explained in "Mixed dilutes,"
below, horses may simutaneously carry more than one dilution gene. Dilution genes which, by themselves, may be confused with cream dilutions include the following:
- Bay dun vs. Buckskin: the action of the Dun gene
The dun gene is a dilution gene that affects both red and black pigments in the coat color of a horse. The dun gene has the ability to affect the appearance of all black, bay, or chestnut -based horses to some degree by lightening the base body coat and suppressing the underlying base color to the...
on bay produce a buckskin-like coat. Additional confusion occurs because in some countries, it is still customary to refer to buckskins as "dun", particularly in the British pony breeds. Bay duns tend to have a flatter coat color, more tan or peanut butter-colored than bronze, and also exhibit primitive markingsPrimitive markings among domestic horses are a group of hair coat markings and qualities associated with primitive breeds, and the dun coat color family in particular. All dun horses possess at least the dorsal stripe but the presence of the other primitive markings varies...
.
- Amber champagne vs. Buckskin: the action of the Champagne gene
The champagne gene is a simple dominant allele responsible for a number of rare horse coat colors. The most distinctive traits of horses with the champagne gene are the hazel eyes and pinkish, freckled skin, which are bright blue and bright pink at birth, respectively...
on bay can also produce a buckskin-like coat. Champagnes can be identified by their freckled skin, hazel eyes, and chocolate (rather than black) points.
- Flaxen chestnut vs. Palomino: Chestnut coats with flaxen manes and tails, such as those found in the Haflinger
The Haflinger is a small, lightweight, four wheel drive, off-road vehicle about 3.5 m long and 1.5 m wide, powered by a 646 cc twin horizontally opposed, rear mounted, air-cooled engine...
breed, can be confused with palominos. However unlike these chestnuts, palominos cannot be true-breeding. Furthermore, even the lightest chestnut will retain "red" character in the hair, rather than gold.
- Gold champagne vs. Palomino: the action of the Champagne gene
The champagne gene is a simple dominant allele responsible for a number of rare horse coat colors. The most distinctive traits of horses with the champagne gene are the hazel eyes and pinkish, freckled skin, which are bright blue and bright pink at birth, respectively...
on chestnut was for many years called pumpkin-skinned palomino. Freckled skin and hazel eyes identify a gold champagne, which can look much like a palomino.
- Pearl vs. Palomino: the action of the pearl gene
The Pearl gene, also known as the "Barlink factor," is a dilution gene that somewhat resembles the cream gene and the champagne gene, but is neither. It is a somewhat rare dilution gene found in the American Quarter Horse, American Paint Horse, and Peruvian Paso. The same mutation appears in...
only occurs on a red coat when the pearl allele is homozygous. In such cases, the red hairs are lightened to an apricot color.
- Pseudo double-dilute vs. Cremello: A horse that has one cream allele and one pearl allele may resemble a homozygous cream, including pinkish skin and blue eyes.
- White vs. Double dilute: White horses with blue or dark eyes and pink skin are born white and remain so throughout life. Cremello and isabelline horses that bleach out in the sun may approach a near-white shade, but have some skin pigment, exhibited by a slightly more peach skin tone and blue-eyed creams have a less vivid shade of blue when compared to that of an unpigmented blue-eye.
- Gray vs. Double dilute: Gray horses are born a normal color and grow progressively lighter in their coat, while double-dilute creams do not. Grays that are not affected by a dilution gene do not have blue eyes or pink skin unless they are due to white markings. There are, however, records of palominos, buckskins, smoky blacks, and double-dilute creams that also carry the gray gene.
Mixed dilutes
If a horse carries more than one type of dilution gene, additional cream mimics and other unique colors may occur. The combined effects of champagne and a single cream gene can be hard to distinguish from a double-dilute cream. Freckled skin and greenish eyes, or pedigree knowledge can yield clues, though the mystery can also be solved with a DNA test.
The
pearl geneThe Pearl gene, also known as the "Barlink factor," is a dilution gene that somewhat resembles the cream gene and the champagne gene, but is neither. It is a somewhat rare dilution gene found in the American Quarter Horse, American Paint Horse, and Peruvian Paso. The same mutation appears in...
or "barlink factor" is a recessive gene that affects only red pigment. When a single copy each of pearl and cream are present, the effect is quite similar to cremello. Dilutes combining the
pearl geneThe Pearl gene, also known as the "Barlink factor," is a dilution gene that somewhat resembles the cream gene and the champagne gene, but is neither. It is a somewhat rare dilution gene found in the American Quarter Horse, American Paint Horse, and Peruvian Paso. The same mutation appears in...
with one copy of the cream gene are known as "pseudo-double dilutes" and produce a cream dilute phenotype that includes pale skin and blue/green eyes. DNA tests and patience are effective in determining which is the case.
Some of the terms used to describe these combinations include:
- Dunalino, yellow dun, or palomino dun: a chestnut-based coat with one cream allele and at least one dun allele. The points are reddish, but the body coat is a paler, flatter shade of gold and primitive markings are visible.
- Dunskin, buckskin dun, or buttermilk dun: a bay-based coat with one cream allele and at least one dun allele. These are quite difficult to tell apart from ordinary duns. They are a slightly paler shade, and retain their dark points and primitive markings.
- Cream dun, Cremello dun or linebacked cremello: a blue-eyed cream horse also carrying the dun gene. The primitive markings
Primitive markings among domestic horses are a group of hair coat markings and qualities associated with primitive breeds, and the dun coat color family in particular. All dun horses possess at least the dorsal stripe but the presence of the other primitive markings varies...
associated with the dun color are usually quite visible, especially on horses with a bay or black base coat.
- Smoky grulla, silver grulla or smoky black dun: a black-based coat with one cream allele and at least one dun allele. The effect is of an extra-pale grulla.
- Double-cream champagne: any blue-eyed cream horse that also carries the champagne gene. The champagne traits are, in the few known individuals, not visible. The skin is quite pink.
- Amber cream or Buckskin champagne: a bay-based coat with one cream allele and at least one champagne allele
The champagne gene is a simple dominant allele responsible for a number of rare horse coat colors. The most distinctive traits of horses with the champagne gene are the hazel eyes and pinkish, freckled skin, which are bright blue and bright pink at birth, respectively...
. The skin and eyes have champagne traits such as skin mottling, while the coat is a pale buff color. The points are a soft, pale grayish-chocolate.
- Classic cream or Smoky black champagne: a black-based coat with one cream allele and at least one champagne allele. is also an acceptable term. Like an amber cream, they retain champagne traits in the skin and eyes, and range from pale buff to pale chocolatey-gray. Even though the coat is black-based, the mane and tail tend to be darker.
- Gold cream: chestnut-based coat with one cream allele and at least one champagne allele. Formerly referred to as "ivory champagne." The champagne traits remain in the skin and eyes, and the coat is an all-over ivory color.
- Sable cream or Brown buckskin champagne: brown
Seal brown is a hair coat color of horses characterized by a near-black body color, with a black mane, tail and legs, and reddish or tan areas around the eyes, muzzle, behind the elbow and in front of the stifle...
-based coat with one cream allele and at least one champagne allele. The coat color falls between amber and classic cream.
- Silver buckskin: bay-based coat with one cream allele and at least one silver dapple allele. The effect varies, as silver dapple does not act on red coats, but the buckskin's golden tone is somewhat lost.
- Silver smoky black: black-based coat with one cream allele and at least one silver allele. The effect varies from chestnut-like to silver black-like. Lighter eyes can help with identification.
Inheritance and expression
The cream
locusIn the fields of genetics and evolutionary computation, a locus is the specific location of a gene or DNA sequence on a chromosome. A variant of the DNA sequence at a given locus is called an allele. The ordered list of loci known for a particular genome is called a genetic map...
is on
exonAn exon is a nucleic acid sequence that is represented in the mature form of an RNA molecule after either portions of a precursor RNA have been removed by cis-splicing or by two or more precursor RNA molecules have been ligated by trans-splicing. The mature RNA molecule can be a messenger RNA or...
2 of the
MATPMembrane-associated transporter protein is a protein that in humans is encoded by the SLC45A2 gene.-Further reading:...
gene; a
single nucleotide polymorphismA single-nucleotide polymorphism is a DNA sequence variation occurring when a single nucleotide — A, T, C, or G — in the genome differs between members of a species...
results in an
aspartic acidAspartic acid is an α-amino acid with the chemical formula HO2CCHCH2CO2H. The carboxylate anion of aspartic acid is known as aspartate...
-to-
asparagineAsparagine is one of the 20 most common natural amino acids on Earth. It has carboxamide as the side chain's functional group. It is not an essential amino acid...
substitutionIn genetics, a missense mutation is a point mutation in which a single nucleotide is changed, resulting in a codon that codes for a different amino acid. This can render the resulting protein nonfunctional...
(N153D). The DNA test offered by various laboratories detects this mutation. The MATP gene encodes a
proteinProteins are organic compounds made of amino acids arranged in a linear chain and folded into a globular form. The amino acids in a polymer chain are joined together by the peptide bonds between the carboxyl and amino groups of adjacent amino acid residues...
illustrated to have roles in melanogenesis in
humanHumans are bipedal primates belonging to the species Homo sapiens in Hominidae, the great ape family. They are the only surviving member of the genus Homo. Humans have a highly developed brain, capable of abstract reasoning, language, introspection, and problem solving...
s,
miceA mouse is a small mammal belonging to the order of rodents. The best known mouse species is the common house mouse . It is also a popular pet. The American white-footed mouse and the deer mouse also sometimes live in houses. In some places, certain kinds of field mice are also common...
, and medaka. Mice affected by a condition homologous to cream exhibit irregularly-shaped
melanosomeIn a biological cell, a melanosome is an organelle containing melanin, the most common light-absorbing pigment found in the animal kingdom.Cells that contain melanosomes are called melanocytes, and also the retinal pigment epithelium cells, whereas cells that have merely engulfed the melanosomes...
s, which are the organelles within melanocytes that directly produce pigment.
Genes in horses such as
FrameLethal White Syndrome , also called Overo Lethal White Syndrome , Lethal White Overo , and Overo Lethal White Foal Syndrome , is an autosomal genetic disorder most prevalent in the American Paint Horse. Affected foals are born after the full 11-month gestation and externally appear normal, though...
and
Sabino1Sabino is a group of white spotting patterns in horses that affect the skin and hair. A wide variety of irregular color patterns are accepted as Sabino. In the strictest sense, "sabino" refers to the white patterns produced by the Sabino1 gene, for which there is a DNA test...
produce white spotting by interrupting or limiting the migration of melanocytes from the
neural crestThe neural crest, a transient component of the ectoderm, is located in between the neural tube and the epidermis of an embryo during neural tube formation...
, while the cream mutation affects the nature of the pigments produced by melanocytes. Therefore the skin, eyes, and hair of horses with the cream mutation do not lack melanocytes, melanosomes, or melanins, but rather exhibit hypomelanism.
Prior to the mapping of the cream gene, this locus was titled
C for "color". There are two alleles in the series: the recessive,
wildtypeWild type refers to the phenotype of the typical form of a species as it occurs in nature. Originally, the wild type was conceptualized as a product of the standard, "normal" allele at a locus, in contrast to that produced by a non-standard, "mutant" allele...
allele
C and the incomplete dominant
CCr. The
CCr allele represents the N153D MATP mutation.
- C/C recessive homozygotes
Zygosity is the similarity of genes for a trait in an organism. If both genes are the same, the organism is homozygous for the trait. If both genes are different, the organism is heterozygous for that trait...
are not affected by cream and have no true cream traits.
- C/CCr heterozygotes have one cream allele, and one wildtype non-cream allele. Only red pigment in the hair is diluted, as seen in buckskins and palominos.
- CCr/CCr homozygotes (homozygous creams) have no wildtype non-cream alleles. The red and black pigment in the hair are diluted to cream, the eyes are light blue and the skin is rosy pink.
Cream was first formally studied by Adalsteinsson in 1974, who reported that the inheritance of palomino and buckskin coat colors in Icelandic horses followed a "semi-dominant" or incomplete dominant model. Adalsteinsson also noted that in heterozygotes, only the red pigment (
pheomelaninMelanin is a class of compounds found in plants, animals, and protists, where it serves predominantly as a pigment. The class of pigments are derivatives of the amino acid tyrosine. Many melanins are insoluble salts and show affinity to water...
) was diluted.
The discovery that the palomino coat color was inextricably linked to the cream coat color was very significant. At one time, double dilutes, particularly cremellos, were barred from registration by many breed organizations. Cremello was thought by some to be a white or albino coloring and a potential genetic defect. There also were known health implications of albinism in humans, and cultural prejudices; while a heroic figure such as
Roy RogersRoy Rogers , was a singer and cowboy actor, as well as the namesake of the Roy Rogers Restaurants chain. He and his second wife Dale Evans, his golden palomino Trigger, and his German Shepherd Dog, Bullet, were featured in over one hundred movies and The Roy Rogers Show...
rode a golden palomino, the "Albino" in
Mary O'HaraMary O'Hara Alsop was an American author and screenwriter.-Biography:Mary O'Hara Alsop was born July 10, 1885 in Cape May Point, New Jersey, the third child of Reverend Dr. Reese Fell Alsop and Mary Lee Spring. O'Hara, who was named after her maternal grandmother, Mary O'Hara Spring , grew up in...
's
Thunderhead portrayed a horse with a freakish defect. These coat colors carried vastly different cultural significance. Some of the research that took place nearly thirty years after Adalsteinsson's studies was directly supported by breed registries that barred blue eyed creams.
Cryptic creams
The cream gene's preferential effect on red pigment has not yet been explained. The champagne dilution affects both black and red pigments equally, the silver dapple affects only black pigment, and pearl exhibits a recessive mode of inheritance and only affects red pigment. Unlike the cream gene, pearl does not seem to affect the mane and tail to a greater extent than the body coat, a feature of cream that is most vividly illustrated in the palomino coat color. This characteristic of the cream gene is also unexplained. The disparity in effects on red and black pigments is easy to identify in buckskins, with their black points, but it is also visible in C
Cr/C
Cr homozygotes: perlinos (homozygous cream on a bay coat) often retain points that are a darker shade of cream.
This unusual feature enables what are called
cryptic creams. A certain percentage of dark bay,
seal brownSeal brown is a hair coat color of horses characterized by a near-black body color, with a black mane, tail and legs, and reddish or tan areas around the eyes, muzzle, behind the elbow and in front of the stifle...
, and
blackBlack is a hair coat color of horses in which the entire hair coat is black. Black is a relatively uncommon coat color, and novices frequently mistake dark chestnuts or bays for black. However, some breeds of horses, such as the Friesian horse, Murgese and Ariegeois are almost exclusively black...
horses exhibit such subtle dilution of their coats as to be misregistered. In the study that mapped the cream gene, three horses registered as seal brown, dark bay or bay were actually smoky black and buckskin. This is one way by which the cream gene is transmitted through generations without being identified. Horses born palomino, buckskin, and smoky black, but also carry the
grayGray or grey is a coat color of horses characterized by progressive silvering of the colored hairs of the coat. Most gray horses have black skin and dark eyes; unlike many depigmentation genes, gray does not affect skin or eye color Their adult hair coat is white, dappled, or white intermingled...
gene, have a hair coat that turns white as they age and are usually registered as "gray" rather than as their birth color. This is particularly a common occurrence in the
ConnemaraConnemara , which derives from Conmhaicne Mara , is a district in the west of Ireland consisting of a broad peninsula between Killary Harbour and Kilkieran Bay in the west of County Galway or south west Connacht...
breed. Horses sold after turning fully gray may surprise breeders by producing golden or cream offspring.
This effect - stronger expression on red pigment - is also seen in coat pattern genes in horses. In general,
white markingsMarkings on horses usually are distinctive white areas on an otherwise dark base coat color. Most horses have some markings, and they help to identify the horse as a unique individual. Markings are present at birth and do not change over the course of the horse's life...
are more pervasive in chestnuts than in non-chestnuts, to the extent that homozygous non-chestnuts (which carry the "Extension" (E) gene and may also carry the Agouti gene) were more modestly marked than non-chestnuts heterozygous for the
E gene. This effect has also been identified and studied in the
Leopard complexThe leopard complex is a group of genetically-related coat patterns in horses. These patterns range from progressive increases in interspersed white hair similar to graying or roan to distinctive, Dalmatian-like leopard spots on a white coat. Secondary charactersitics associated with the leopard...
patterns.
Analogous conditions in other animals
The MATP gene is highly-conserved, especially among mammals. The human MATP gene is 82% identical to the mouse MATP gene, 79% identical to the rat MATP gene, 35% to the zebrafish version, and 30% identical to the fruitfly MATP gene. The gene is best-known in humans as being the location of a mutation that results in human type IV oculocutaneous albinism (OCA4). Type IV oculocutaneous albinism, like other types of human albinism, results in hypopigmentation of the skin and eyes, with increased rates of skin cancer and reduced visual acuity. None of these effects are associated with the equine cream gene. Other human MATP polymorphisms result in normal pigment variations, specifically fair skin, light eyes, and light hair in Caucasian populations.
A polymorphism on the mouse MATP gene is known to be the cause of the
underwhite coat color phenotype. The phenotype was first identified in the 1960s, and since then has been mapped successfully. Affected individuals have a reduction in eye and coat pigmentation, and irregularly-shaped melanosomes.
See also
- Equine coat color genetics
Equine coat color genetics determine a horse's coat color. There are many different coat colors possible, but all colors are produced by the action of only a few different genes. The simplest genetic default color of all domesticated horses can be described as either "red" or "non-red", depending...
- Equine coat color
Horses exhibit a diverse array of coat colors and distinctive markings. A specialized vocabulary has evolved to describe them. Color is one of the first things that is noticed about a horse...
- White (horse)
White horses are born white and stay white throughout their life. White horses may have brown, blue, or hazel eyes. "True white" horses, especially those that carry one of the dominant white genes, are rare...
- Gray (horse)
Gray or grey is a coat color of horses characterized by progressive silvering of the colored hairs of the coat. Most gray horses have black skin and dark eyes; unlike many depigmentation genes, gray does not affect skin or eye color Their adult hair coat is white, dappled, or white intermingled...
- Palomino
Palomino is a coat color in horses, consisting of a gold coat and white mane and tail. Genetically, the palomino color is created by a single allele of a dilution gene called the cream gene working on a red base coat...
- Buckskin (horse)
- Dun gene
The dun gene is a dilution gene that affects both red and black pigments in the coat color of a horse. The dun gene has the ability to affect the appearance of all black, bay, or chestnut -based horses to some degree by lightening the base body coat and suppressing the underlying base color to the...
- Champagne gene
The champagne gene is a simple dominant allele responsible for a number of rare horse coat colors. The most distinctive traits of horses with the champagne gene are the hazel eyes and pinkish, freckled skin, which are bright blue and bright pink at birth, respectively...
- Silver dapple gene
The silver dapple gene is a dilution gene that affects the black base coat color. It will typically dilute a black mane and tail to flaxen, and a black body to a shade of brown or chocolate. It is responsible for a group of coat colors in horses called "silver dapple" in the west, or "taffy" in...
- Albinism
Albinism is a form of hypopigmentary congenital disorder, characterized by a partial or total lack of melanin pigment in the eyes, skin and hair, or more rarely...
- Leucism
- Lethal white syndrome
Lethal White Syndrome , also called Overo Lethal White Syndrome , Lethal White Overo , and Overo Lethal White Foal Syndrome , is an autosomal genetic disorder most prevalent in the American Paint Horse. Affected foals are born after the full 11-month gestation and externally appear normal, though...