How do Fawnequin and Brindlequin patterns occur?
Fawnequin and Brindlequin patterns occur because the Harlequin gene is unique among merle modifiers: it affects both eumelanin (black/blue/chocolate pigment) and phaeomelanin (red/yellow/tan pigment). While typical merle modifiers only impact dark pigments, the Harlequin gene’s ability to affect red/yellow pigment means that if a dog inherits the merle and harlequin genes alongside the genes for fawn or brindle coats, its entire coat is altered.
Because the Harlequin gene removes dilute background pigment entirely and turns it pure white, the fawn or brindle coloring is confined only to the patches where the dog would have normally had solid black spots if it were a standard blue/black merle.
Here is the specific genetic breakdown for how each pattern occurs:
Fawnequin Genetics A Fawnequin is a harlequin dog with tan (sable/fawn) patches on a white base, often with some black patches where black merling would normally show. For this to occur, the dog must inherit:
• The Fawn Base: The dog must carry the genetic instructions for a fawn coat, which includes homozygous recessive alleles (a
y
a
y
) on the A-locus and recessive alleles (k
y
k
y
) on the K-locus that allows the fawn color to be visibly expressed. They also typically carry the masking gene (E
m
E
m
• Merle and Harlequin: The dog must also inherit one copy of the Merle gene (M) and one copy of the Harlequin gene (H).
• Resulting Genotype Example: A
y
A
y
E
m
E
m
HhMm.
Brindlequin Genetics: A Brindlequin is a harlequin dog with brindle-striped patches on a white base. The brindle striping appears broken up and patchy due to the merle gene. For this pattern to occur, the dog must inherit:
• The Fawn Base: Like the Fawnequin, the dog must have the sable/fawn base (a
y
a
y
) in order for the brindle striping to show all over the body.
• The Brindle Gene: The dog must inherit the brindle mutation, which allows brindle striping to appear over the fawn base coat (often represented as the K
br
allele on the K-locus).
• Merle and Harlequin: The dog must also inherit the heterozygous Merle (Mm) and Harlequin (Hh) genes, which break up the brindle patches and turn the background white.
• Resulting Genotype Example: a
y
a
y
k
br
k
br
HhMm.