OMIA:001972-9796 : Coat colour, dun in Equus caballus (horse) |
In other species: ass (donkey) , Przewalski's horse
Categories: Pigmentation phene
Links to possible relevant human trait(s) and/or gene(s) in OMIM: 601621 (gene)
Mendelian trait/disorder: yes
Mode of inheritance: Autosomal dominant
Disease-related: no
Key variant known: yes
Year key variant first reported: 2016
Species-specific symbol: D, d1, d2
Species-specific description:
"Dun is a wild-type coat color in horses characterized by pigment dilution with a striking pattern of dark areas termed primitive markings." (Imsland et al., 2016). Primitive markings usually appear as a dorsal stripe and bars on the legs. Primitive markings usually appear as a dorsal stripe and bars on the legs. These primitive markings were discussed at some length by Darwin (1859) (chap 5, pp. 163-167).
[IT thanks Haley Rutstein, working under the guidance of Professor Ernie Bailey, for contributions to this entry in April 2024]
Inheritance:
By studying the results of matings in Icelandic horses, Adalsteinsson (1978) concluded that "a dominant dilution gene, D, converts bay to yellow dun with dark mane and tail, chestnut to yellow dun and dun mane and tail, and black to blue dun (mouse, grullo)".
Imsland et al., 2016 described three alleles at the D locus: D for dilution, d1 for no dilution but primitive markings, and d2 for no dilution and no primitive markings. D and d1 have dominant modes of inheritance. The d2 allele is recessive. The d2 allele is most prevalent among the most common horse breeds, however the nature of the variants suggested that D and d1 were ancestral forms of the gene among horses prior to domestication.
Mapping: Imsland et al. (2016) "mapped the Dun locus to a region on horse chromosome 8 (chr. 8: 18,061,745–18,482,196) using microsatellite markers and then fine-mapped the locus with a 27-SNP panel to a 200-kb region containing only one gene, TBX3"
Molecular basis: Following mapping, the candidate region was DNA sequenced leading to the discovery of a pair of insertions associated with the D and d1 alleles. The D allele appears as an 8 bp insertion followed downstream by a 1609 bp insertion. The d1 allele, described as having no dilution but showing primitive markings, appears as an 8 bp insertion followed downstream by a 1610 bp insertion. The d2 allele is described as having no dilution and no primitive markings. The d2 allele is characteristic of the genome reference sequence, EquCab 3.0. Imsland et al. (2016) showed that "pigment dilution in Dun horses is due to radially asymmetric deposition of pigment in the growing hair caused by localized expression of the T-box 3 (TBX3) transcription factor in hair follicles, which in turn determines the distribution of hair follicle melanocytes." Furthermore, both d1 and d2 are “regulatory mutations impairing TBX3 expression in the hair follicle, resulting in a more circumferential distribution of melanocytes and pigment granules in individual hairs” resulting in “a more intensely pigmented phenotype”.
Breeds:
American Trotter (Horse) (VBO_0000899),
Arab (Horse) (VBO_0000905),
Curly Horse (Horse) (VBO_0000943),
Faeroes Pony (Horse) (VBO_0017117),
Fjord (Horse) (VBO_0000961),
Gotland Pony (Horse) (VBO_0000974),
Icelandic Horse (Horse) (VBO_0000991),
Mongolian (Horse) (VBO_0001021),
Quarter Horse (Horse) (VBO_0001057),
Shetland Pony (Horse) (VBO_0001066),
Swedish Warmblood (Horse) (VBO_0001077).
Breeds in which the phene has been documented. (If a likely causal variant has been documented for the phene, see the variant table breeds in which the variant has been reported).
Associated gene:
Symbol | Description | Species | Chr | Location | OMIA gene details page | Other Links |
---|---|---|---|---|---|---|
TBX3 | T-box 3 | Equus caballus | 8 | NC_009151.3 (20646967..20661149) | TBX3 | Homologene, Ensembl , NCBI gene |
Variants
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WARNING! Inclusion of a variant in this table does not automatically mean that it should be used for DNA testing. Anyone contemplating the use of any of these variants for DNA testing should examine critically the relevant evidence (especially in breeds other than the breed in which the variant was first described). If it is decided to proceed, the location and orientation of the variant sequence should be checked very carefully.
Since October 2021, OMIA includes a semiautomated lift-over pipeline to facilitate updates of genomic positions to a recent reference genome position. These changes to genomic positions are not always reflected in the ‘acknowledgements’ or ‘verbal description’ fields in this table.
OMIA Variant ID | Breed(s) | Variant Phenotype | Gene | Allele | Type of Variant | Source of Genetic Variant | Reference Sequence | Chr. | g. or m. | c. or n. | p. | Verbal Description | EVA ID | Year Published | PubMed ID(s) | Acknowledgements |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
1029 | Non-dun without primitive markings | TBX3 | nd2 | regulatory | Naturally occurring variant | EquCab3.0 | 8 | allele is represented by the reference genome EquCab3.0 | 2016 | 26691985 | [IT thanks Haley Rutstein, working under the guidance of Professor Ernie Bailey, for contributions to this entry in April 2024] | |||||
1701 | Curly Horse (Horse) Fjord (Horse) Icelandic Horse (Horse) Quarter Horse (Horse) | Dun | TBX3 | D | regulatory | Naturally occurring variant | EquCab3.0 | 8 | NC_009151.3:g.[20665796_20665797insCCTTCTGGC;20665807_20665808ins[1609]] | 2016 | 26691985 | [IT thanks Haley Rutstein, working under the guidance of Professor Ernie Bailey, for contributions to this entry in April 2024] | ||||
1028 | American Trotter (Horse) Arab (Horse) Curly Horse (Horse) Faeroes Pony (Horse) Gotland Pony (Horse) Mongolian (Horse) Quarter Horse (Horse) Shetland Pony (Horse) Swedish Warmblood (Horse) | Non-dun with primitive markings | TBX3 | nd1 | regulatory | Naturally occurring variant | EquCab3.0 | 8 | NC_009151.3:g.[20665796_20665797insCCTTCTGGC;20665807_20665808ins[1610]] | 2016 | 26691985 | [IT thanks Haley Rutstein, working under the guidance of Professor Ernie Bailey, for contributions to this entry in April 2024] |
Cite this entry
Nicholas, F. W., Tammen, I., & Sydney Informatics Hub. (2024). OMIA:001972-9796: Online Mendelian Inheritance in Animals (OMIA) [dataset]. https://omia.org/. https://doi.org/10.25910/2AMR-PV70
References
Note: the references are listed in reverse chronological order (from the most recent year to the earliest year), and alphabetically by first author within a year.
2024 | Durward-Akhurst, S.A., Marlowe, J.L., Schaefer, R.J., Springer, K., Grantham, B., Carey, W.K., Bellone, R.R., Mickelson, J.R., McCue, M.E. : |
Predicted genetic burden and frequency of phenotype-associated variants in the horse. Sci Rep 14:8396, 2024. Pubmed reference: 38600096. DOI: 10.1038/s41598-024-57872-8. | |
2021 | Cieslak, J., Brooks, S.A., Wodas, L., Mantaj, W., Borowska, A., Sliwowska, J.H., Ziarniak, K., Mackowski, M. : |
Genetic background of the Polish primitive horse (Konik) coat color variation-new insight into dun dilution phenotypic effect. J Hered 112:436-442, 2021. Pubmed reference: 34432873. DOI: 10.1093/jhered/esab034. | |
2019 | Mackowski, M., Wodas, L., Brooks, S.A., Cieslak, J. : |
TBX3 and ASIP genotypes reveal discrepancies in officially recorded coat colors of Hucul horses. Animal 13:1811-1816, 2019. Pubmed reference: 30614426. DOI: 10.1017/S1751731118003506. | |
2016 | Imsland, F., McGowan, K., Rubin, C.J., Henegar, C., Sundström, E., Berglund, J., Schwochow, D., Gustafson, U., Imsland, P., Lindblad-Toh, K., Lindgren, G., Mikko, S., Millon, L., Wade, C., Schubert, M., Orlando, L., Penedo, M.C., Barsh, G.S., Andersson, L. : |
Regulatory mutations in TBX3 disrupt asymmetric hair pigmentation that underlies Dun camouflage color in horses. Nat Genet 48:152-8, 2016. Pubmed reference: 26691985. DOI: 10.1038/ng.3475. | |
1978 | Adalsteinsson, S. : |
Inheritance of yellow dun and blue dun in the Icelandic toelter horse. J Hered 69:146-8, 1978. Pubmed reference: 731005. DOI: 10.1093/oxfordjournals.jhered.a108913. | |
1859 | Darwin, C.R. : |
On the Origin of Species by Means of Natural Selection John Murray, London , 1859. |
Edit History
- Created by Frank Nicholas on 22 Dec 2015
- Changed by Frank Nicholas on 22 Dec 2015
- Changed by Frank Nicholas on 06 Aug 2016
- Changed by Frank Nicholas on 12 Feb 2019
- Changed by Imke Tammen2 on 14 Apr 2024
- Changed by Imke Tammen2 on 03 Jun 2024