The Russian Blue is genetically defined by absolute restriction to a single phenotype: blue solid (a/a + d/d), representing homozygosity at both the Agouti locus (non-agouti, a/a) and the Dilution locus (d/d), producing a uniformly diluted, non-patterned coat. This mandatory dual homozygosity means that any Russian Blue carrying a dominant allele at either the A locus (A/-) or D locus (D/-) cannot express the breed-defining phenotype and is a disqualifying fault in FIFe and most major registries. Feline genetics and EMS code calculator tools for RUS are therefore minimally complex at the color level, though breeders must still genotype for hidden chocolate (b) alleles that — while not expressed in the all-blue standard — must not produce non-blue offspring.
Common recessive carriers
All Russian Blues are fixed homozygous d/d (dilute) and a/a (non-agouti/solid). Chocolate (b) alleles are reported as present in some RUS lines; while b/b would produce chocolate, no b-series dilutes (lilac, etc.) are accepted. Any non-blue phenotype arising from a Russian Blue pairing indicates either a registration error or undisclosed outcrossing and is a disqualifying fault.
Breed-specific restrictions
Only the blue solid phenotype (EMS: RUS a) is recognized under FIFe standard. All other colors — black, white, colourpoint, tabby patterns, silver, bicolor — are categorically excluded. Russian White and Russian Black are recognized as separate varieties in some non-FIFe registries (e.g., CCCA in Australia) but are NOT valid under FIFe. The breed is strictly fixed for a/a (non-agouti) and d/d (dilute) genotypes.
Pattern quirks
No pattern variants are accepted. Although ghost tabby striping may be faintly visible in kittens (a transient phenotype from residual phaeomelanin during development), adult Russian Blues must present as solid blue with no visible tabby pattern. Smoke, silver, bicolor, and white-spotting are all disqualifying.
RUS aBlue (solid) — the only recognized colorRUS a (kitten)Blue solid — note: ghost tabby barring in kittens is genetically non-agouti (a/a) and resolves with maturityFree online tool to predict kitten coat colors based on Mendelian genetics. Select the breed and appearance of sire and dam to see color probabilities.
Enter the appearance of both parents to calculate color predictions.