Co-Locus Genetics
Cocoa French Bulldog Gene
The complete guide to the co-locus cocoa gene (HPS3). How it differs from B-locus chocolate, how it creates Isabella, and which DNA panels detect it.
Model Cocoa OutcomesWhat Is the Cocoa Gene?
The co-locus is a color gene discovered in French Bulldogs that produces a lighter, cocoa-toned brown. It works alongside the B-locus to create the ultra-rare Isabella color.
Co Allele (Dominant)
The capital Co allele is dominant and produces normal pigment expression. Dogs with Co/Co or Co/co show their base color without cocoa lightening. The dominant allele does not create the cocoa phenotype.
co Allele (Recessive Cocoa)
The lowercase co allele is recessive. A dog needs two copies (co/co) to show the cocoa effect. This allele lightens brown pigment to a cocoa or taupe shade. When combined with b/b, it produces Isabella.
Cocoa vs. B-Locus Chocolate
Two different genes can produce brown pigment in French Bulldogs. Understanding the difference is critical for accurate breeding and color prediction.
How Cocoa Creates Isabella
Isabella is the result of stacking three rare recessive genes. The co-locus is the final piece that transforms lilac into the ultra-rare Isabella shade.
D-Locus (d/d)
Dilute lightens all pigment. Black becomes blue, brown becomes lighter.
B-Locus (b/b)
Chocolate turns black pigment to brown. Combined with dilute, this creates lilac.
Co-Locus (co/co)
Cocoa further lightens the brown pigment. Combined with b/b and d/d, this creates Isabella â the lightest champagne-brown shade.
Test for Cocoa Before You Breed
Our DNA Calculator includes the co-locus alongside B, D, E, K, A, S, M, and L. Model Isabella, cocoa, and chocolate outcomes with full accuracy.
Open the DNA CalculatorFrequently Asked Questions
What is the cocoa gene in French Bulldogs?
The cocoa gene (co-locus) is a recently discovered color gene in French Bulldogs that affects brown pigment production through the HPS3 gene. When a dog carries two copies of the recessive cocoa allele (co/co), it produces a lighter, more cocoa-toned brown coat compared to the classic B-locus chocolate. The cocoa gene is distinct from the B-locus and requires specific DNA testing to detect.
How does cocoa differ from B-locus chocolate?
B-locus chocolate (b/b, TYRP1 gene) produces a rich, deep brown color that affects the coat, nose, and paw pads uniformly. Co-locus cocoa (co/co, HPS3 gene) produces a lighter, more muted cocoa or taupe-toned brown. A dog can carry both genes â when b/b and co/co are present together, the result is Isabella, an even lighter champagne-brown shade. B-locus chocolate is testable on all major panels; cocoa requires newer panels that include the HPS3 test.
Can my DNA test detect the cocoa gene?
It depends on which DNA panel you used. Older panels from some labs did not include the co-locus (HPS3) test. Embark, Animal Genetics, and DDC now offer cocoa testing as part of their updated French Bulldog panels. If your dog looks chocolate but tested as B/B (non-chocolate) on an older panel, request a re-test with the cocoa gene included. The dog may actually be co/co.
What is a cocoa French Bulldog?
A cocoa French Bulldog is a dog with the co/co genotype at the co-locus. It shows a lighter brown or cocoa-toned coat compared to classic B-locus chocolate. The nose and pads may also be a lighter brown. Cocoa Frenchies are sometimes confused with chocolate or liver-colored dogs. DNA testing is the only way to distinguish between B-locus chocolate, co-locus cocoa, and dogs that carry both.
How does cocoa create Isabella?
Isabella is created when a dog carries both the B-locus chocolate allele (b/b) AND the co-locus cocoa allele (co/co), along with the D-locus dilute allele (d/d). The B-locus turns black to brown, the co-locus lightens that brown further, and the D-locus dilutes it to a champagne or taupe shade. The result is the ultra-rare Isabella color â essentially 'double chocolate' with dilution.
Should I test for cocoa before breeding?
Yes. If you are breeding for rare colors or selling puppies as specific color variants, testing for the co-locus is essential. A dog that appears chocolate but tests B/B may actually be co/co, which completely changes breeding predictions. Testing for both B-locus and co-locus ensures you can accurately predict chocolate, cocoa, lilac, and Isabella outcomes in your litters.