How do breeders use the A-series to identify fawns?

Breeders use the A-series (specifically the ASIP or Agouti gene) to identify fawn Great Danes by testing for the presence of the sable allele (a 

y

 ). This genetic variant codes for a reddish-yellow base coat (phaeomelanin) and dark-tipped hairs (eumelanin), which together form the foundation of the Fawn and Brindle colors.

To fully identify and predict a fawn coat, breeders must look at how a dog’s A-series interacts with the K-locus (the CBD103 gene):

• Showing the Fawn Color: In order for the fawn color coded on the A-series to be visibly expressed, the dog must lack the dominant black gene. Specifically, it must possess two copies of the recessive K 

y

  allele (K 

y

 K 

y

 ) at the K-locus. If the K-locus allows expression, a dog with one or two copies of the a 

y

  allele will visually appear fawn (or brindle, if the brindle modifier K 

Br

  is also present.

• Finding Hidden Carriers: If a dog possesses the dominant K 

B

  If an allele is on its K-locus, its coat will be a solid color (like black, blue, or chocolate), and the A-locus will be completely overridden. Because this dominant gene easily hides the a 

y

  Breeders use A-series DNA testing to determine whether their solid-colored dogs are secretly carrying the fawn trait and can pass it to their offspring.

• Clarifying Spotted Coats: Breeders also use A-series testing to help identify the underlying coat color of dogs that have extreme white spotting patterns, where the white may obscure the distribution of the fawn pigment.

When breeders receive DNA test results for the A-series, a dog with an a 

y

 /a 

y

  The genotype is homozygous for the fawn/sable trait.