Dun gene

Last updated September 03, 2024

A bay dun, also called a "classic" or "zebra" dun

A “blue” dun, or grullo

A red dun

The dun gene is a dilution gene that affects both red and black pigments in the coat color of a horse. The dun gene lightens most of the body while leaving the mane, tail, legs, and primitive markings the shade of the undiluted base coat color. A dun horse always has a dark dorsal stripe down the middle of its back, usually has a darker face and legs, and may have transverse striping across the shoulders or horizontal striping on the back of the forelegs. Body color depends on the underlying coat color genetics. A classic "bay dun" is a gray-gold or tan, characterized by a body color ranging from sandy yellow to reddish brown. Duns with a chestnut base may appear a light tan shade, and those with black base coloration are a smoky gray. Manes, tails, primitive markings, and other dark areas are usually the shade of the undiluted base coat color. The dun gene may interact with all other coat color alleles.

Taxonomic distribution

Dun is believed to be the ancestral or wild type color of horses.^[1] Many equines appearing in prehistoric cave paintings such as in Chauvet Cave are dun,^[2] and several closely related species in the genus Equus show dun characteristics. These include the Przewalski's horse,^[3] onager, kiang, African wild ass, an extinct subspecies of plains zebra, the quagga,^[4] and an extinct subspecies of horse, the tarpan. Zebras can also be considered a variant of dun where the dilution is so extreme it turns the hair nearly white, and the primitive markings (like the striped leg barring) extend across the entire body.^[4]

Neither the non-dun1 nor the non-dun2 mutations were found in any other equids.^[4]

Cave painting at Lascaux: Dun is thought to be a wild type coloration Lascaux2.jpg — Cave painting at Lascaux: Dun is thought to be a wild type coloration

Color traits

Dorsal stripe on a red dun IslandFuchsfalbe.jpg — Dorsal stripe on a red dun

The dun gene has a dilution effect, lightening the body coat, but has less of an effect on the primitive markings and on the point coloration of the mane, tail, ears, and legs.

Dun visibly affects all the three base colors, bay (bay, classic, or zebra dun), black (mouse dun or grullo), and Chestnut (red dun). It is more difficult to recognize when combined with other dilution genes or if affected by gray.^[5] Shades include:

Dun, also called bay dun, classic dun, or zebra dun is the most common type of dun, and has a tan or gold body with black mane, tail, and primitive markings. Genetically, the horse has an underlying bay coat color, acted upon by the dun gene.^[6]^[7]
Red dun, also called claybank, is a light tan coat with reddish instead of black points and primitive markings. Genetically, the horse has an underlying chestnut coat color, acted upon by the dun gene. Thus, as there is no black on the horse to be affected, the undiluted underlying color is red.^[6]^[7]
Grullo or grulla, also called blue dun or mouse dun, is a smoky, blue-gray to mouse-brown color and can vary from light to dark. They consistently have black points and they often have a dark or black head. The primitive markings are usually all black. Genetically, the horse has an underlying black coat color, acted upon by the dun gene.^[6]^[7]

Another characteristic of the dun gene are primitive markings.^[5] Dun traits include the following:

Dorsal stripe down the center of the back, along the spine, seen almost universally on duns
Horizontal striping on the back of forelegs, common on most duns, although at times, rather faint
Facial mask, a darker area around the nasal bone and forehead, sometimes making the head close to the undiluted color, some patterns colloquially called "Cobwebbing."^[1]
Transverse stripe, a crosswise stripe along the shoulders perpendicular to the dorsal stripe, very common in donkeys, less common in horses, and if present, often faint, usually only visible on a short summer coat, if at all.^[1]
Frosting: light hairs found on either side of the mane and on both sides of the dock of the tail.

Other variations result from the interplay of additional genes:

Chestnut + dun + cream gene (single copy) = "dunalino" or "palomino dun"
Bay + dun + cream gene (single copy) = "dunskin" or "buckskin dun"

A single copy of the cream gene on a black base coat does not significantly lighten black hair, though it may have a subtle effect,^[8] and thus a single copy generally has no visible effect on a grullo, either. Conversely, double copies of the cream gene create very light-colored horses (cremello, perlino, and smoky cream). Thus, if a horse with two cream dilution alleles also carries the dun gene, it also will be cream-colored, with primitive markings not visible to any significant degree.

Dorsal striping alone does not guarantee the horse carries the dun gene. There two types of non-dun, called non-dun1 and non-dun2. Non-dun1 horses have no dun color dilution but may keep primitive markings, while non-dun2 horses have neither the dun color dilution nor primitive markings.^[9]

The Fjord horse breed, which is predominantly dun, uses unique Norwegian-based terminology to distinguish between the different shades of dun horses. "Brown dun", or brunnblakk is a zebra dun, rødblakk is a red dun, grå - literally "gray" - is a grullo, buckskin duns are called ulsblakk or white dun, and a "dunalino" (dun + palomino) is called a "yellow dun" or gulblakk. A cremello, perlino or smoky cream is called "white" or kvit.^[10]

Dun mimics

Historically, before modern genetic studies distinguished between alleles, diluted colors were sometimes lumped together and simply called "dun".^[11]

The dun gene, when on a "bay dun" horse, can closely resemble buckskin, in that both colors feature a light-colored coat with a dark mane and tail. In particular, buckskins with non-dun 1 primitive markings can easily be confused with dun.^[11]^: 32 Genetically, a bay dun is a bay horse with the dun gene. A buckskin is bay horse with the addition of the cream gene, causing the coat color to be diluted from red to gold, usually without primitive markings. Visually, a bay dun is a tan-gold color, somewhat darker and less vivid than the more cream or gold buckskin, and duns always possess primitive markings.^[12] Today, pedigree analysis, DNA testing, studying possible offspring, and the vividness of primitive markings are used to determine whether a horse is a dun.

A red dun may also be confused with a perlino , which is genetically a bay horse with two copies of the cream gene, which creates a horse with a cream-colored body but a reddish mane and tail. However, perlinos usually are significantly lighter than red dun and have blue eyes.

Grullos are sometimes confused with roans or grays. However, unlike blue roan, dun has no intermingled black and white hairs, and unlike a true gray, which also intermingles light and dark hairs, the color does not change to a lighter shade as the horse ages. With a dun, the hair color is one solid shade and remains so for life.

To further confuse matters, it is possible for a horse to carry both dun and cream dilution genes; such horses with golden buckskin coloring and a complete set of primitive markings are referred to as a "buckskin dun" or a "dunskin". On such horses, the light-shaded primitive markings are most noticeable during the summer months, when the winter hair sheds. A palomino that also carries dun, showing primitive dorsal striping or leg bars indicative of a red dun may be called a "dunalino."

Countershading such as light dorsal stripes resulting from the presence of the gene nd1 (see section below) may be difficult to detect on light-colored horses.

Genetics

There are three known alleles of the dun gene: dun (D), produces dilution and primitive markings. Non-dun1 (d1) horses do not have dun dilution but may exhibit some primitive markings. Non-dun2 (d2) horses have neither dilution nor primitive markings.^[4] Dun is a dominant gene; however, at least one study found a statistically significant variation in the shade of dilution depending on whether one or two copies of the dun gene are present.^[13] Two non-dun parents cannot produce a dun foal. Horses that are non-dun1 d1/d1 or d1/d2 may have some asymmetry in pigment distribution, producing primitive markings, but to a lesser degree than dun horses. Homozygous non-dun1/non-dun1 horses typically have clearer primitive markings than heterozygous d1/d2 horses. The primitive markings from non-dun1 are more visible on a bay or chestnut horse; they blend in on a black. A horse with two copies of non-dun2 lacks primitive markings.^[4]

Dun has a stronger effect than other dilution genes in that it acts on any coat color. In contrast, the silver dapple gene acts only on black-based coats, and the cream gene is an incomplete dominant which must be homozygous to be fully expressed, and when heterozygous is only visible on bay and chestnut coats, and then to a lesser degree.^[5]

The dun dilution effect is caused by pigment only being placed in a part of each hair. Specifically, hairs from diluted areas only have pigment along one side of them, while hairs from darker parts such as the dorsal stripe have pigment all the way around.^[4]

Genetic analysis and DNA sequencing results published in 2015 link dun color to the T-box 3 (TBX3) transcription factor. When functional, it creates dun coloring, including the primitive markings, and when recessive, a horse is not dun. In humans and lab mice, TBX3 is critical to development. Abnormalities are linked to a collection of developmental defects called ulnar–mammary syndrome, and the null allele (being unable to produce any TBX3 at all) is thought to be embryonic lethal.^[14] In non-dun horses, the TBX3 protein is still functional, and is still produced in most cells, but not expressed in the hair cortex. Where the coat is diluted, the color is not uniform throughout each hair, but rather is more intense on the outward-facing side of the hair shaft and lighter underneath. In the darker areas, where the primitive markings occur, the hair shaft is of uniform color. One of the researchers involved in the study said it could be called a "microscopic spotting pattern".^[11]^: 31 This phenomenon is new to science and has not been observed in rodents, primates, or carnivores.^[15]

The location of TBX3 expression may also determine the striping pattern of zebras.^[15]

Dorsal stripe and light guard hairs on a dun horse
Transverse shoulder stripe

Non-dun alleles

There are two forms of non-dun color, non-dun1 and non-dun2, caused by different mutations. Non-dun1 horses have some primitive markings, while non-dun2 horses do not.

Prior to domestication of the horse, dun, non-dun1, and the leopard complex are thought to have been the wild type modifiers of the base colors bay and black for wild horses. It is thought that the non-dun2 genetic mutation (as well as the development of chestnut base color) occurred after domestication. Ancient DNA from a horse that lived about 43,000 years ago, long before horses were domesticated, carried both dun and non-dun1 genes.^[1]

The non-dun mutations appear to "disrupt the function of a transcriptional enhancer regulating TBX3 expression in a specific subset of hair bulb keratinocytes during hair growth." The region deleted in non-dun2 is predicted to include binding sites for the transcription factors ALX4 and MSX2, which are both known to be involved in hair follicle development. TBX3 was significantly downregulated in non-dun horses compared to dun horses, while the neighboring gene, TBX5 , was expressed in about the same amount. In dun horses, the pattern of TBX3 expression mirrored the pattern of pigment deposition in the hair, that is, TBX3 was found wherever the pigment was not. TBX3 was not found in the hair cortex keratinocytes from non-dun horses nor in those from the dorsal stripe of dun horses. However, all of the horses had a thin outer layer of the hair where TBX3 was expressed. Two markers of mature melanocytes, KIT and MITF, were found only in the pigmented areas of the hair. This indicates that the hair follicles of dun and non-dun horses have different distributions of pigment-producing cells. KITLG encodes KIT ligand, a molecule required for melanocyte migration and survival in the skin and hair follicle. Keratinocytes expressing KITLG were found all the way around the hair in non-dun horses, but only on the pigmented side in dun horses. The region where KITLG was not expressed was similar to, but not exactly the same as, the region where TBX3 was expressed. TBX3 is not thought to directly affect KITLG expression.^[4]

Both non-dun1 and non-dun2 are found in a region of equine chromosome 8 whose only gene is TBX3. Non-dun1 has a guanine where dun has an adenine at chromosome 8 base pair 18,226,905, which appears to be sufficient to cause non-dun1 coloration. In addition, non-dun1 has another single nucleotide polymorphism compared to the version of dun that is most common in domestic horses, where a guanine in dun is replaced with thymine in non-dun1 at chr. 8: 18,227,267. However, that SNP was also found in some dun Estonian native horses, so is not necessary for dun. Non-dun2 has a 1,609 bp deletion and another very near 8 bp deletion. Comparison with TBX3 in other species showed that the non-dun2 deletion is a more derived allele. Nucleotide diversity across the flanking regions of chromosome 8 for the various alleles indicates that the non-dun2 mutation most likely occurred on a chromosome that already had non-dun1.^[4]

Related Research Articles

<span class="mw-page-title-main">Roan (color)</span> Coat color found in many animals

Roan is a coat color found in many animals, including horses, cattle, antelope, cats and dogs. It is defined generally as an even mixture of white and pigmented hairs that do not "gray out" or fade as the animal ages. There are a variety of genetic conditions which produce the colors described as "roan" in various species.

Palomino is a genetic color in horses, consisting of a gold coat and white mane and tail; the degree of whiteness can vary from bright white to yellow. The palomino color derived from the inter-breeding of Spanish horses with those from the United States. Genetically, the palomino color is created by a single allele of a dilution gene called the cream gene working on a "red" (chestnut) base coat. Palomino is created by a genetic mechanism of incomplete dominance, hence it is not considered true-breeding. However, most color breed registries that record palomino horses were founded before equine coat color genetics were understood as well as they are today, therefore the standard definition of a palomino is based on the visible coat color, not heritability nor the underlying presence of the dilution gene.

A dilution gene is 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:

<span class="mw-page-title-main">Bay (horse)</span> Hair coat color of horses

Bay is a hair coat color of horses, characterized by a reddish-brown or brown body color with a black point coloration on the mane, tail, ear edges, and lower legs. Bay is one of the most common coat colors in many horse breeds.

Buckskin is a colour of horse. Buckskins coloring is a hair coat color referring to a color that resembles certain shades of tanned deerskin. Similar colors in some breeds of dogs are also called buckskin. The horse has a tan or gold colored coat with black points. Buckskin occurs as a result of the cream dilution gene acting on a bay horse. Therefore, a buckskin has the Extension, or "black base coat" (E) gene, the agouti gene (A) gene, which restricts the black base coat to the points, and one copy of the cream gene (CCr), which lightens the red/brown color of the bay coat to a tan/gold.

<span class="mw-page-title-main">Brindle</span> Coat coloring pattern in some animals

Brindle is a coat coloring pattern in animals, particularly dogs, cattle, guinea pigs, cats, and, rarely, horses. It is sometimes described as "tiger-striped", although the brindle pattern is more subtle than that of a tiger's coat.

A gray horse has a coat color characterized by progressive depigmentation of the colored hairs of the coat. Most gray horses have black skin and dark eyes; unlike some equine dilution genes and some other genes that lead to depigmentation, gray does not affect skin or eye color. Gray horses may be born any base color, depending on other color genes present. White hairs begin to appear at or shortly after birth and become progressively more prevalent as the horse ages as white hairs become intermingled with hairs of other colors. Graying can occur at different rates—very quickly on one horse and very slowly on another. As adults, most gray horses eventually become completely white, though some retain intermixed light and dark hairs.

<span class="mw-page-title-main">Cream gene</span> Gene for several horse coat colors

The cream gene is responsible for a number of horse coat colors. Horses that have the cream gene in addition to a base coat color that is chestnut will become palomino 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 black or a smoky cream. Cream horses, even those with blue eyes, are not white horses. Dilution coloring is also not related to any of the white spotting patterns.

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 coat color is also affected: any hairs that would have been red are gold, and any hairs that would have been black are chocolate brown. If a horse inherits the champagne gene from either or both parents, a coat that would otherwise be chestnut is instead gold champagne, with bay corresponding to amber champagne, seal brown to sable champagne, and black to classic champagne. A horse must have at least one champagne parent to inherit the champagne gene, for which there is now a DNA test.

Equine coat color genetics determine a horse's coat color. Many colors are possible, but all variations are produced by changes in only a few genes. Bay is the most common color of horse, followed by black and chestnut. A change at the agouti locus is capable of turning bay to black, while a mutation at the extension locus can turn bay or black to chestnut.

The Fjord or Norwegian Fjord Horse is a relatively small but very strong horse breed from the mountainous regions of western Norway. It is an agile breed of light draught horse build. It is always dun in colour, with five variations in shade recognised in the breed standard. One of the world's oldest breeds, it has been used for hundreds of years as a farm horse in Norway, and in modern times is popular for its generally good temperament. It is used both as a harness horse and under saddle.

<span class="mw-page-title-main">Grullo</span> Color of horses in the dun family

Grullo or grulla is a color of horses in the dun family, characterized by tan-gray or mouse-colored hairs on the body, often with shoulder and dorsal stripes and black barring on the lower legs. The genotype for grulla horses is a black base with dun dilution. In this coloration, each individual hair is mouse-colored, unlike a roan, which is composed of a mixture of dark and light hairs. The several shades of grulla are informally referred to with a variety of terms, including black dun, blue dun, slate grulla, silver grulla or light grulla, silver dun, or lobo dun. Silver grulla may also refer to a grulla horse with silver dapple, regardless of shade.

<span class="mw-page-title-main">Chestnut (horse color)</span> Horse coat color

Chestnut 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. Chestnut is characterized by the absolute absence of true black hairs. It is one of the most common horse coat colors, seen in almost every breed of horse.

Horses exhibit a diverse array of coat colors and distinctive markings. A specialized vocabulary has evolved to describe them.

<span class="mw-page-title-main">White horse</span> Horse coat color

A white horse is born predominantly white and stays white throughout its life. A white horse has mostly pink skin under its hair coat, and may have brown, blue, or hazel eyes. "True white" horses, especially those that carry one of the dominant white (W) genes, are rare. Most horses that are commonly referred to as "white" are actually "gray" horses whose hair coats are completely white. Gray horses may be born of any color and their hairs gradually turn white as time goes by and take on a white appearance. Nearly all gray horses have dark skin, except under any white markings present at birth. Skin color is the most common method for an observer to distinguish between mature white and gray horses.

Black is a hair coat color of horses in which the entire hair coat is black. It is not uncommon to mistake dark chestnuts or bays for black.

Smoky black or black carrying cream is a coat color of horses which has the same phenotype as black. Smoky black is produced by the action of a heterozygous cream gene on an underlying black coat color. Therefore, smoky black is a member of the cream family of coat color dilutions, and found in horse populations that have other cream-based colors such as palomino, buckskin, perlino, cremello and smoky cream. All smoky blacks must have at least one parent with the cream gene, and a smoky black can only be verified through DNA testing or parentage. Smoky black has been mistaken for faded black, dark bay or brown, grullo or even liver chestnut.

<span class="mw-page-title-main">Sooty horse</span> Trait characterized by black or darker hairs mixed into a horses coat

A sooty or smutty horse coat color is characterized by black or darker hairs mixed into a horse's coat, typically concentrated along the topline of the horse and less prevalent on the underparts. The effect is especially pronounced on buckskins and palominos. Sootiness is believed to be an inherited trait involving multiple genes, however the details are not yet known. Horses without any visible sooty coloration are termed "clear-coated."

Primitive markings are a group of hair coat markings and qualities seen in several equine species, including horses, donkeys, and asses. In horses, they are associated with primitive breeds, though not limited to such breeds. The markings are particularly associated with the dun coat color family. All dun horses possess at least the dorsal stripe, but the presence of the other primitive markings varies. Other common markings may include horizontal striping on the legs, transverse striping across the shoulders, and lighter guard hairs along the edges of a dark mane and tail.

Seal brown is a hair coat color of horses characterized by a near-black body color; with black points, the mane, tail and legs; but also reddish or tan areas around the eyes, muzzle, behind the elbow and in front of the stifle. The term is not to be confused with "brown", which is used by some breed registries to refer to either a seal brown horse or to a dark bay without the additional characteristics of seal brown.

References

1 2 3 4 "Dun Dilution - Direct Test". Veterinary Genetics Lab, University of California, Davis. Retrieved 2019-04-27.
↑ Pruvost M, et al. (2011-11-07). "Genotypes of predomestic horses match phenotypes painted in Paleolithic works of cave art". PNAS. 108 (46): 18626–30. Bibcode:2011PNAS..10818626P. doi: 10.1073/pnas.1108982108 . PMC 3219153 . PMID 22065780.
↑ "Przewalski's horse". Smithsonian's National Zoo. 25 April 2016. Retrieved 2019-04-26.
1 2 3 4 5 6 7 8
Imsland F, McGowan K, Rubin CJ, Henegar C, Sundström E, Berglund J, et al. (February 2016). "Regulatory mutations in TBX3 disrupt asymmetric hair pigmentation that underlies Dun camouflage color in horses". Nature Genetics. 48 (2): 152–8. doi:10.1038/ng.3475. PMC 4731265 . PMID 26691985.
- "A horse of a different color: Genetics of camouflage and the dun pattern". ScienceDaily (Press release). December 21, 2015.
1 2 3 "Dun Zygosity Test." Veterinary Genetics Lab, University of California, Davis. Web page accessed December 4, 2009
1 2 3 "Introduction to Coat Color Genetics". UC Davis. Retrieved 2019-04-27.
1 2 3 Adalsteinsson S. (May 1978). "Inheritance of yellow dun and blue dun in the Icelandic toelter horse". J Hered. 69 (3): 146–8. doi:10.1093/oxfordjournals.jhered.a108913. PMID 731005.
↑ Cream - Horse Coat Color
↑ "More about Dun and Primitive Markings". Etalon Diagnostics. Retrieved 2019-04-28.
↑ Sponenberg, Phillip. "Color in Fjord Horses". Norwegian Fjord Horse Registry. Retrieved January 20, 2010.
1 2 3 Imsland, Freyja (2015). Monogenic Traits Associated with Structural Variants in Chicken and Horse (PDF) (Thesis). Uppsala. p. 42. ISBN 978-91-554-9295-3. ISSN 1651-6206.
↑ "A Horse Of A Different Color: Buckskins And Duns". Cowgirl Magazine. 15 August 2017. Retrieved 2019-04-28.
↑ Cieslak, Jakub; Brooks, Samantha Ann; Wodas, Lukasz; Mantaj, Weronika; Borowska, Alicja; Sliwowska, Joanna Helena; Ziarniak, Kamil; MacKowski, Mariusz (2021). "Genetic Background of the Polish Primitive Horse (Konik) Coat Color Variation—New Insight into Dun Dilution Phenotypic Effect". Journal of Heredity. 112 (5): 436–442. doi: 10.1093/jhered/esab034 . PMID 34432873.
↑ Frank DU, Emechebe U, Thomas KR, Moon AM (2013-07-02). Dettman R (ed.). "Mouse TBX3 mutants suggest novel molecular mechanisms for Ulnar-mammary syndrome". PLOS ONE. 8 (7): e67841. Bibcode:2013PLoSO...867841F. doi: 10.1371/journal.pone.0067841 . PMC 3699485 . PMID 23844108.
1 2 Waara, Anneli (December 21, 2015). "Genetics of camouflage and the Dun pattern in horses". SciLifeLab, Uppsala University. Retrieved June 26, 2016.

External links

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[UCDavisDun-1] 1 2 3 4 "Dun Dilution - Direct Test". Veterinary Genetics Lab, University of California, Davis. Retrieved 2019-04-27.

[Pruvost2011-2] Pruvost M, et al. (2011-11-07). "Genotypes of predomestic horses match phenotypes painted in Paleolithic works of cave art". PNAS. 108 (46): 18626–30. Bibcode:2011PNAS..10818626P. doi: 10.1073/pnas.1108982108 . PMC 3219153 . PMID 22065780.

[3] "Przewalski's horse". Smithsonian's National Zoo. 25 April 2016. Retrieved 2019-04-26.

[Imsland2015-4] 1 2 3 4 5 6 7 8 Imsland F, McGowan K, Rubin CJ, Henegar C, Sundström E, Berglund J, et al. (February 2016). "Regulatory mutations in TBX3 disrupt asymmetric hair pigmentation that underlies Dun camouflage color in horses". Nature Genetics. 48 (2): 152–8. doi:10.1038/ng.3475. PMC 4731265 . PMID 26691985.
"A horse of a different color: Genetics of camouflage and the dun pattern". ScienceDaily (Press release). December 21, 2015.

[mwAYc] "A horse of a different color: Genetics of camouflage and the dun pattern". ScienceDaily (Press release). December 21, 2015.

[Dun_Zygosity-5] 1 2 3 "Dun Zygosity Test." Veterinary Genetics Lab, University of California, Davis. Web page accessed December 4, 2009

[UCDavisIntro-6] 1 2 3 "Introduction to Coat Color Genetics". UC Davis. Retrieved 2019-04-27.

[Adalsteinsson1978-7] 1 2 3 Adalsteinsson S. (May 1978). "Inheritance of yellow dun and blue dun in the Icelandic toelter horse". J Hered. 69 (3): 146–8. doi:10.1093/oxfordjournals.jhered.a108913. PMID 731005.

[8] Cream - Horse Coat Color

[etalon-9] "More about Dun and Primitive Markings". Etalon Diagnostics. Retrieved 2019-04-28.

[Sponenberg-10] Sponenberg, Phillip. "Color in Fjord Horses". Norwegian Fjord Horse Registry. Retrieved January 20, 2010.

[ImslandThesis-11] 1 2 3 Imsland, Freyja (2015). Monogenic Traits Associated with Structural Variants in Chicken and Horse (PDF) (Thesis). Uppsala. p. 42. ISBN 978-91-554-9295-3. ISSN 1651-6206.

[12] "A Horse Of A Different Color: Buckskins And Duns". Cowgirl Magazine. 15 August 2017. Retrieved 2019-04-28.

[13] Cieslak, Jakub; Brooks, Samantha Ann; Wodas, Lukasz; Mantaj, Weronika; Borowska, Alicja; Sliwowska, Joanna Helena; Ziarniak, Kamil; MacKowski, Mariusz (2021). "Genetic Background of the Polish Primitive Horse (Konik) Coat Color Variation—New Insight into Dun Dilution Phenotypic Effect". Journal of Heredity. 112 (5): 436–442. doi: 10.1093/jhered/esab034 . PMID 34432873.

[14] Frank DU, Emechebe U, Thomas KR, Moon AM (2013-07-02). Dettman R (ed.). "Mouse TBX3 mutants suggest novel molecular mechanisms for Ulnar-mammary syndrome". PLOS ONE. 8 (7): e67841. Bibcode:2013PLoSO...867841F. doi: 10.1371/journal.pone.0067841 . PMC 3699485 . PMID 23844108.

[uppsala-15] 1 2 Waara, Anneli (December 21, 2015). "Genetics of camouflage and the Dun pattern in horses". SciLifeLab, Uppsala University. Retrieved June 26, 2016.

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