What causes a puppy to be a “fawnequin”?

A “fawnequin” puppy is produced when a dog inherits the genetic instructions for a fawn coat alongside both the Merle and Harlequin modifier genes.

Unlike other merle modifiers that only impact dark pigments (eumelanin), the Harlequin gene is unique because it also affects red or yellow pigment (phaeomelanin). This means that if a sable/fawn dog inherits the merle and harlequin genes, the modifiers act upon its entire coat rather than just the dark parts.

For a puppy to be a fawnequin, it must inherit a specific combination of genes:

• The Fawn Base: The puppy must inherit the genetic traits that create a fawn coat. This involves inheriting the recessive alleles on the K-locus (K 

y

 K 

y

 ), which allows the color on the A-locus to be visibly expressed, along with the sable/fawn alleles on the A-locus (A 

y

 A 

y

 ). They also often carry the masking gene (E 

m

 E 

m

• Merle and Harlequin Modifiers: The puppy must also inherit one copy of the Merle gene (M) and one copy of the Harlequin gene (H).

When these genes combine (typically resulting in an A 

y

 A 

y

 E 

m

 E 

m

 HhMm genotype), the Harlequin modifier turns the dog’s background coat pure white, leaving tan (sable) patches. These tan patches appear in the exact locations where a standard blue/black merle would have had black spots. Additionally, the puppy will usually have some black patches interspersed exactly where normal black merle would have appeared.