The Tabby gene on chromosome A1 accounts for most tabby patterns seen in domestic cats, including those patterns seen in most breeds. The dominant allele TaM produces mackerel tabbies, and the recessive Tab produce classic (sometimes referred to as blotched) tabbies. The gene responsible for this differential patterning has been identified as transmembrane aminopeptidase Q (Taqpep, ). A threonine to asparagine substitution at residue 139 (T139N) in this protein is responsible for producing the tabby phenotype in domestic cats. In cheetahs, a base pair insertion into exon 20 of the protein replaces the 16 C-terminal residues with 109 new ones (N977Kfs110), generating the king cheetah coat variant.
