The canine A locus (ASIP) regulates the distribution of eumelanin (black/brown) and pheomelanin (yellow/red) in the coat. It is not a simple recessive system: it is modulated by two independent promoters (the ventral promoter, VP, and the hair-cycle-specific promoter, HCP), whose combined activity generates the pattern. The sesame colour of the Shiba inu (red hairs with dark tips on the back) corresponds to specific allelic combinations of these promoters. It is a colour trait, not a disease.

The sesame pattern is characteristic of the Shiba inu. In the study by Belyakin et al. (2022) the red sesame dogs carried the diplotype VP2-HCP1/VP2-HCP3. Population frequencies by breed: limited data.

- Red hairs with black tips distributed over the back (sesame)\n- Dark dorsal overtones of variable extent\n- No clinical manifestations: it is a colour trait

The A locus was described in the dog in 1957 (Little) and for decades different alleles (A^y, a^w, a^s, a^t, a) were proposed with inconsistent and controversial nomenclature. In 2021, Bannasch et al. showed that the patterns are explained by regulatory variants in two promoters (VP and HCP) of the ASIP gene and proposed a new nomenclature: DY > SY > AG > BS > BB > a. That same system made it possible to explain the sesame pattern of the Shiba inu, and Belyakin et al. (2022) showed that red sesame is associated with a heterozygous promoter diplotype VP2-HCP1/VP2-HCP3.

- Sesame is a colour trait, not a defect or a disease.\n- Knowing the promoter haplotypes (VP/HCP) of the breeding animals makes it possible to plan the litter's pattern.\n- Tests based only on associated markers may give discordant results; interpret with caution.\n- Do not over-select for a pattern if this reduces the breed's genetic variability.

The canine A locus is a modular system of promoters (VP and HCP) and not a classic series of coding mutations; some commercial tests use markers in linkage disequilibrium, with the possibility of discordant results (Bannasch et al. 2021). The Shiba inu sesame is an aesthetic trait with no pathological implication.

1. Bannasch DL et al. 2021. Dog colour patterns explained by modular promoters of ancient canid origin. Nature Ecology & Evolution. PMID: 34385618
2. Belyakin SN et al. 2022. ASIP Promoter Variants Predict the Sesame Coat Color in Shiba Inu Dogs. Veterinary Sciences. PMID: 35622750
3. OMIA:000201-9615. Coat colour, agouti in Canis lupus familiaris. Online Mendelian Inheritance in Animals.