Colour pattern roan

The roan coat pattern in dogs is characterized by the presence of pigmented patches that are distributed in an apparently uniform manner within areas of the coat that would normally express white patches.

Definition

The trait refers to a coloration pattern in which areas of the body that would normally exhibit a white coloration are altered, resulting in the appearance of pigmented spots in these areas. These spots are generally evenly distributed throughout the body, although they can also occur irregularly. Dogs that develop this phenotype are usually born with a white pattern of coloration, and during the first weeks of life, the characteristic pigmented areas of this pattern emerge. The variant identified is located in the USH2A gene, which encodes the usherin-2A protein. It is speculated that this protein could be involved in the pigmentation pathway and, in addition, could be related to hearing. However, further research is needed to support this claim.

Genetic basis

The presence of one or two copies of the variant results in the expression of this coloration pattern in dogs. However, for this phenotype to be visible, it is necessary that a gene related to the formation of white spots is also expressed, as is the case of the variant in the MITF gene that leads to the piebald coloration pattern.

Other relevant information

The Dalmatian breed appears to have a modified version of the roan coloration pattern, which is distinguished by the clear definition of the pigmented spots in the white coat areas. It should be noted that in some dogs with a red/yellow base color, it is sometimes difficult to differentiate this pattern from other mottled coloration patterns. This trait is also called by other names, such as "blue" in the Australian Cattle Dog or "Belton" in the English Setter. Breeds that commonly exhibit this pattern include the Australian Cattle Dog, English Cocker Spaniel, Wirehaired Pointing Griffon and German Shorthaired Pointer.

Bibliography

Brancalion L, Haase B, Mazrier H, et al. Roan, ticked and clear coat patterns in the canine are associated with three haplotypes near usherin on CFA38. Anim Genet. 2021 Apr;52(2):198-207.

Kawakami T, Jensen MK, Slavney A, et al. R-locus for roaned coat is associated with a tandem duplication in an intronic region of USH2A in dogs and also contributes to Dalmatian spotting. PLoS One. 2021 Mar 23;16(3):e0248233.