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Phenotype: Brindle is a vertical striped coat pattern accompanied by abnormal hair texture.
Mode of Inheritance: X-linked, semi-dominant
Alleles: N = Normal or non-brindle, BR1 = Brindle1
Breeds appropriate for testing: Quarter Horse, Paint Horse
Explanation of Results:
- Males only have one X chromosomes where females have two, therefore possible genotypes will differ by sex.
- Female horses with N/N genotype and male horses with N genotype (males only have one X chromosome) will not have the brindle coat texture and cannot transmit this brindle variant to their offspring.
- Female horses with BR1/N genotype will display the brindle coat texture. They may transmit this brindle variant to 50% of their offspring.
- Female horses with the BR1/BR1 genotype will have a sparse mane and tail, but will not display the brindle coat texture. They will transmit this brindle variant to all of their offspring.
- Male horses with the BR1 genotype will have a sparse mane and tail, but will not display the brindle coat texture. They will transmit this brindle variant to all of their offspring.
The brindle coat texture is characterized by vertical stripes on the coat that show a change in texture and may show a change in pigmentation. To avoid confusion with the spontaneous, not heritable brindle pattern associated with chimerism, the coat texture pattern has been named brindle 1 (BR1). The stripes form a vertical pattern from the back to the sides of horses that is characterized by changes in hair structure as well as pigmentation. The hairs from the stripes are less straight and unrulier than hairs from the normally pigmented and textured coat. The BR1 phenotype is variable in that in some females, the predominant feature is the coat texture change while in others it is the striped pigmentation. Males with BR1 mutation have sparse manes and tails but not the texture pattern. The BR1 phenotype can occur on any color background and shows seasonal changes (summer versus winter), with winter coat often having a “moth-eaten” appearance.
The molecular basis of a striped coat texture pattern that produces a brindle phenotype in a lineage of Quarter Horses has been identified by Dr. Tosso Leeb's research laboratory in Switzerland and in collaboration with members of the VGL team. Investigation of the brindle coat texture identified a mutation in the intron of the gene MBTPS2 (c.1437+4T>C). The BR1 phenotype has an X-linked, semi-dominant mode of inheritance, meaning that females with one copy look different than those with two. Females with 1 copy of the BR1 mutation have the brindle phenotype. Females with 2 copies of the BR1 mutation (BR1/BR1) have sparse manes and tails but not the striped coat texture pattern. Males only have one X chromosome so (BR1) males are similar to the females with two copies in that they have sparse manes and tails but are lacking the striped coat texture pattern.
This test for the brindle coat texture can help owners and breeders identify homozygous females (animals with two copies of the variant) or males with one copy of this brindle coat texture variant if they are attempting to breed for the brindle coat texture.
Species
Breed
| Test Result | Brindle Coat Texture |
|---|---|
| N/N | No copies of the BR1 mutation detected in female horse. |
| N | No copies of the BR1 mutation detected in male horse. |
| N/BR1 | One copy of the BR1 mutation detected in female horse. Striping pattern is expected. |
|
BR1/BR1 |
Two copies of the BR1 mutation detected in female horse. |
| BR1 | One copy of the BR1 mutation detected in male horse. Horse may display sparse mane and tail but no visible striping pattern. |
Murgiano, L., Waluk, D. P., Towers, R., Wiedemar, N., Dietrich, J., Jagannathan, V., Drögemüller, M., Balmer, P., Druet, T., Galichet, A., Penedo, M. C., Müller, E., Roosje, P., Welle, M., & Leeb, T. (2016). An Intronic MBTPS2 Variant Results in a Splicing Defect in Horses with Brindle Coat Texture. G3: Genes|Genomes|Genetics, 6(9), 2963-2970. doi: 10.1534/g3.116.032433
