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Equus caballus, horse: phenotypes

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Silver coat color in the horse

Brunberg E, Andersson L, Cothran G, Sandberg K, Mikko S, Lindgren G. A missense mutation in PMEL17 is associated with the Silver coat color in the horse. BMC Genet. 2006 Oct 9;7:46.

Phenotypic description of Silver colored horses.

Phenotypic description of Silver colored horses.
A. A Black Silver Icelandic horse. A genetically black horse that exhibits the typical silver phenotype with a dark body with dapples and a shiny white mane and tail. Photo: Tim Kvick.
B. Two Black Silver Rocky Mountain Horses. Photo: Bob Langrish.
C. A Brown Silver Morgan horse. A genetically brown horse that shows the silver phenotype with the mane and tail diluted from black to white and the lower legs diluted from black to dark greyish. Photo: Laura Behning.
D. The legs of a Brown Silver horse. The lower legs are diluted from black to greyish. Photo: Laura Behning.

Phenotypic description of Silver colored foals

Phenotypic description of Silver colored foals.
A. A Silver colored Icelandic horse foal. Silver foals are generally very pale on the body with white mane and tail. Photo: Elsa Storgärds.
B. A striped hoof of a Silver colored Icelandic horse foal. Photo: Tim Kvick.
C. White eyelashes of a Silver colored Rocky Mountain Horse colt. Photo: Unknown.

A chestnut Morgan horse that carry the Silver mutation

A chestnut Morgan horse that carry the Silver mutation.
This particular individual (Amanda's Suzie Q) indicate that the Silver mutation in horses has little or no effect on pheomelanin (as mane does not seem to be diluted). Photo: Anthony Domire JR.

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Champagne dilution in horses

Cook D, Brooks S, Bellone R, Bailey E. Missense mutation in exon 2 of SLC36A1 responsible for champagne dilution in horses. PLoS Genet. 2008 Sep 19;4(9):e1000195.

Effect of Champagne gene action on base coat colors of horses

Effect of Champagne gene action on base coat colors of horses (chestnut, bay, and black).
A) Chestnut – horse only produces red pigment.
B) Chestnut diluted by Champagne=Gold Champagne.
C) Bay – black pigment is limited to the points (e.g. mane, tail, and legs) allowing red pigment produced on the body to show.
D) Bay diluted by Champagne=Amber Champagne.
E) Black – red and black pigment produced, red masked by black.
F) Black diluted by Champagne=Classic Champagne.

Champagne Eye and Skin traits.

Champagne Eye and Skin traits. A, B and C) Eye and skin color of foals. D and E) Eye color and skin mottling of adult horse.

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Dominant white (W) horses

Haase B, Brooks SA, Schlumbaum A, Azor PJ, Bailey E, Alaeddine F, Mevissen M, Burger D, Poncet PA, Rieder S, Leeb T. Allelic heterogeneity at the equine KIT locus in dominant white (W) horses. PLoS Genet. 2007 Nov;3(11):e195.

Dominant White Phenotype in Horses

Dominant White Phenotype in Horses
(A) Franches-Montagnes mare with little residual pigmentation.
(B, C) Dominant white Franches-Montagnes stallion showing partial depigmentation as a colt and almost complete depigmentation at 4 years of age.
(D) Dominant white Thoroughbred stallion.
(E) Dominant white Arabian stallion.
(F) Camarillo White Horse.
(G) Immunohistochemistry using a polyclonal KIT antibody on a skin biopsy from a solid-colored horse. Blue staining indicates KIT expression throughout the epidermis. Melanin produced by melanocytes is visible as brown granules.
(H) Immunohistochemistry on a skin biopsy of a white horse. Note the weak blue staining and the complete absence of melanocytes and melanin. The bars correspond to 50 μm.

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Chestnut horses

Rendo F, Iriondo M, Manzano C, Estonba A. Identification of horse chestnut coat color genotype using SNaPshot. BMC Res Notes. 2009 Dec 16;2:255.

The Cantabrian Coast horse breeds of the Iberian Peninsula have mainly black or bay colored coats, but alleles responsible for a chestnut coat color run in these breeds and occasionally, chestnut horses are born. Chestnut coat color is caused by two recessive alleles, e and ea, of the melanocortin-1 receptor gene, whereas the presence of the dominant, wild-type E allele produces black or bay coat horses. Because black or bay colored coats are considered as the purebred phenotype for most of the breeds from this region, it is important to have a fast and reliable method to detect alleles causing chestnut coat color in horses.

Horse chestnut coat

The four native breeds analyzed. (a) Pottoka and (b) Jaca Navarra ponies; (c) Euskal Herriko Mendiko Zaldia and (d) Burguete heavy horse breeds.

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Silver (chocolate) coat color and MCOA in horses

Andersson LS, Juras R, Ramsey DT, Eason-Butler J, Ewart S, Cothran G, Lindgren G. Equine Multiple Congenital Ocular Anomalies maps to a 4.9 megabase interval on horse chromosome 6. BMC Genet. 2008 Dec 19;9:88.

Silver colored rocky mountain horse

A Silver colored Rocky Mountain Horse. The typical shiny white mane and tail as well as a slightly diluted body color with dapples is seen in this genetically black Silver colored horse. The phenotype is caused by dilution of eumelanin in the hair to white or grey. The dilution is most visible in the long hairs of the mane and tail. The horse has also been diagnosed with MCOA (Multiple Congenital Ocular Anomalies).

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White Spotting Phenotypes in Horses

Hauswirth R et al. Mutations in MITF and PAX3 Cause "Splashed White" and Other White Spotting Phenotypes in Horses PLoS Genet. 2012 Apr;8(4):e1002653.

Splashed white horses from Quater family

Phenotypes of splashed white horses from a Quarter Horse family. Note that the expression of the phenotype is quite variable. Splashed white may be caused by different mutations, even within closely related horses.
(A) Splashed white bay horse. The unpigmented areas are relatively small, but the horse has blue eyes.
(B) Typical expression of the splashed white phenotype in a chestnut horse with blue eyes.
(C) A splashed white chestnut horse with normal eye color and a relatively small blaze.
(D) Splashed white coat color and brown eyes in a chestnut horse.
(E, F) Two horses carrying both the PAX3C70Y and MITFprom1 alleles with typical splashed white phenotypes. Horses carrying one copy of either PAX3C70Y and/or MITFprom1 show overlapping phenotypes. None of the horses in this figure carry the EDNRBI118K (overo) allele.

Phenotypes of horses with different combinations of splashed white alleles

Phenotypes of horses with different combinations of splashed white alleles. (A) American Paint Horse with a very pronounced depigmentation phenotype. In addition to being homozygous for the MITFprom1 allele, it also carries a private allele at the KIT gene (p.H40Q), which may enhance the depigmentation phenotype. The functional significance of the p.H40Q variant is unclear at the moment.
(B) This Quarter Horse is also homozygous for the MITFprom1 allele, but has substantially more residual pigmentation than the horse shown in panel A.
(C) A Trakehner horse homozygous for the MITFprom1 allele.
(D) A completely white horse with multiple splashed white alleles.
(E) Quarter Horse with the rare MITFC280Sfs*20 allele. This horse has a very pronounced splashed white phenotype with blue eyes and a largely unpigmented head and belly.
(F) A compound heterozygote for two different MITF mutant alleles is completely white. None of the horses in this figure carry the EDNRBI118K (overo) allele.

Macchiato coat color phenotype in a Franches-Montagnes stallion

Macchiato coat color phenotype in a Franches-Montagnes stallion. Note the pronounced depigmentation on the body in addition to the large white blaze on the head, the white legs, and the blue eyes. This horse has a bay basic coat color.

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Graying in Horses

Sundström E et al. Copy number expansion of the STX17 duplication in melanoma tissue from Grey horses. BMC Genomics. 2012 Aug 2;13:365.

The Grey horse phenotype.

The Grey horse phenotype. (A) Grey horse with a dark foal. Photo: Meike Pachner.
(B) A late greying Connemara horse, showing only very few signs of hair greying by the age of 14 years. Photo: Jenny Hagenblad.

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Different morpological types in horses

Dall'Olio S et al. Analysis of horse myostatin gene and identification of single nucleotide polymorphisms in breeds of different morphological types. J Biomed Biotechnol. 2010;2010. pii: 542945.

Horses of extreme and opposite morphological types

Horses of extreme and opposite morphological types: Heavy Draft (brachymorphic type or heavy) and (b) Italian Trotter (dolichomorphic type or light).

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Leopard Complex Spotting in the Horse

Bellone RR, Holl H, Setaluri V, Devi S, Maddodi N, Archer S, Sandmeyer L, Ludwig A, Foerster D, Pruvost M, Reissmann M, Bortfeldt R, Adelson DL, Lim SL, Nelson J, Haase B, Engensteiner M, Leeb T, Forsyth G, Mienaltowski MJ, Mahadevan P, Hofreiter M, Paijmans JL, Gonzalez-Fortes G, Grahn B, Brooks SA. Evidence for a Retroviral Insertion in TRPM1 as the Cause of Congenital Stationary Night Blindness and Leopard Complex Spotting in the Horse. PLoS One. 2013; 8(10): e78280.

Horses of extreme and opposite morphological types

Congenital stationary night blindness is associated with homozygosity for leopard complex spotting in horses.
(A) lp/lp horses do not display a leopard complex spotting pattern and are not night blind as evidenced by normal ERGs.
(B) LP/lp horses display one of several characteristic spotting patterns that vary in the amount of un-pigmented hairs in the coat and have pigmented spots (“leopard spots”) in the un-pigmented area. These horses are not night blind as evidenced by normal ERGs.
(C) LP/LP horses displaying the characteristic homozygous patterns with varying amounts of white on the coat with few to no “leopard spots”. These horses all have CSNB as evidenced by the “negative” ERG in which the b wave is absent.

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Incontinentia Pigmenti in Horses

Towers RE, Murgiano L, Millar DS, Glen E, Topf A, Jagannathan V, Drögemüller C, Goodship JA, Clarke AJ, Leeb T. A Nonsense Mutation in the IKBKG Gene in Mares with Incontinentia Pigmenti. PLoS One. 2013; 8(12): e81625.

Phenotype of an affected horse.

Phenotype of an affected horse.
Brindled pigmentation and patches of hairless skin are visible. The hairless skin probably represents scarring alopecia following the different stages of skin lesions described. The patterns of hyperpigmentation and the skin alterations follow the lines of Blaschko.

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Melanoma and Pigmentation of Coat and Skin in Grey Horses

Curik I, Druml T, Seltenhammer M, Sundström E, Pielberg GR, Andersson L, Sölkner J. Complex Inheritance of Melanoma and Pigmentation of Coat and Skin in Grey Horses. PLoS Genet. Feb 2013; 9(2): e1003248.

Variation of grey levels of the coat, represented by L* values, in six grey Lipizzan horses.

Variation of grey levels of the coat, represented by L* values, in six grey Lipizzan horses.

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