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Dun Dilution
| Acronym: | DD |
| Gene: | TBX3 |
| Mutation: | g.18228333G>T, 1617bp deletion |
| Inheritance: | Autosomal Dominant |
| Sample type: | WBE (Whole Blood EDTA), HA (Hairs - with roots) |
Genetics and characteristics
Horses display a huge variety of distinct coat color patterns that breeders value and they are often caused by a variant in genes responsible for pigment synthesis. Several genes are known to diminish the intensity of the coloration and cause “dilutions”. One of those dilutions is Dun Dilution responsible for the dilution of the base color in combination with primitive markings such as stripes on legs and one along the back. The cause of the dun dilution in horses are two mutations, and hence, there are two variants – the non-dun1 (nd1) mutation, which is caused by the change of a single basepair in the TBX3 gene, and the non-dun2 (nd2) mutation, which is caused by a deletion in the TBX3 gene. The TBX3 gene encodes the T-box 3 transcription factor, a protein that regulates pigment deposition along the radial axis of hair follicles and is expressed in many cell types and has a critical role during development. The dun dilution may differ depending on the base coat the horse has – Red Dun (chestnut), Yellow Dun (bay), Blue Dun, or Grulla (black).
Dun dilution in horses has an autosomal dominant mode of inheritance. That means horses with even one mutated TBX3 gene will dilute to dun coat color, not only horses with two mutated genes. Horses with a specific mutation within the TBX3 gene may also show other characteristics such as primitive bands involving dorsal and shoulder stripes of dark pigmentation and horizontal striping (barring) on the legs. Early detection by genetic testing can help identify carriers of the mutation and help breeders in further selection of mating pairs.
Results Reported As
Test Result |
Interpretation of test result |
Non-dun |
Horse does not have the gene with the mutation and has a normal coat color. |
Non-dun with primitive markings |
Horse does not have the gene with Dun associated mutation, but has one copy of the gene with primitive markings associated mutation. Horse has a normal coat color, but may have primitive markings. |
Dun dilution - carrier of non-dun |
Horse has one copy of the gene with Dun associated mutation and displays a diluted coat color. |
Dun dilution |
Horse has two copies of the gene with Dun associated mutation and displays a diluted coat color. |
References:
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. (2016). Regulatory mutations in TBX3 disrupt asymmetric hair pigmentation that underlies Dun camouflage color in horses. Nature genetics, 48(2), 152–158. https://doi.org/10.1038/ng.3475
Mackowski, M., Wodas, L., Brooks, S. A., Cieslak, J. (2019). TBX3 and ASIP genotypes reveal discrepancies in officially recorded coat colors of Hucul horses. Animal : an international journal of animal bioscience, 13(9), 1811–1816. https://doi.org/10.1017/S1751731118003506