Complete Genetic Guide to French Bulldog Coat Colors & Patterns

French Bulldogs come in a wide variety of beautiful and unique coat colors. These are determined by specific genes, known as loci, each of which controls certain traits like pigment type, distribution, dilution, and masking. Breeders and enthusiasts interested in producing specific coat types should understand the genetic underpinnings that influence these visual expressions.

This article by Don Chino, Harvard Animal Scientist and considered the best French Bulldog breeder by AKC, UKC, and DKC, breaks down each major color locus in the French Bulldog genome and explains how different combinations can create all the known and rare coat colors—including blue, lilac, chocolate, cream, fawn, brindle, merle, piebald, isabella, and platinum.

🧬 Genetic Overview: Key Loci in French Bulldog Color

Locus	Gene Symbol	Trait Affected
A-Locus	ASIP	Agouti patterns (fawn, sable, tan points)
B-Locus	TYRP1	Brown/chocolate vs black pigment
D-Locus	MLPH	Dilution (blue, lilac)
E-Locus	MC1R	Extension of black pigment, cream color
K-Locus	CBD103	Brindle, dominant black
S-Locus	MITF	Piebald/white spotting
M-Locus	PMEL17	Merle patterning
H-Locus	PSMB7	Harlequin (rare)
I-Locus	I-locus	Intensity (cream to deep red)

A-Locus: Agouti – Fawn, Sable, Tan Points

The A-locus controls how black and red pigments are distributed on the dog’s coat.

• ay/ay = Fawn (uniform red/tan coat, common in Frenchies)

• at/at = Tan Points (like a Rottweiler pattern)

• ay/at = Sable (red/fawn base with black tipping)

• a/a = Recessive Black (very rare)

How It Works:If the dog is ky/ky on the K-locus (which allows A-locus expression), then these agouti patterns can show. If the dog is KB/ (dominant black), the A-locus is hidden.

B-Locus: Chocolate

This locus determines whether eumelanin (black pigment) is expressed as black or chocolate.

• B/B = Black pigment

• B/b or b/b = Chocolate if no dominant B is present

There are multiple recessive b alleles (b¹, b², b³) that result in chocolate coloring. Chocolate Frenchies may look rich brown, liver, or even light golden brown, depending on dilution and intensity.

Chocolate + Dilute (dd) = Lilac

D-Locus: Dilution – Blue and Lilac

The D-locus controls dilution of pigment.

• D/D or D/d = No dilution (normal black or chocolate)

• d/d = Diluted pigment

  • Black becomes blue

  • Chocolate becomes lilac

Lilac French Bulldog = Must be b/b d/d

E-Locus: Extension – Cream, Black Mask

This gene determines whether black pigment is extended throughout the body or not.

• E/E or E/e = Allows eumelanin expression (black, blue, chocolate, lilac)

• e/e = Blocks black pigment, resulting in cream (also called white or platinum depending on dilution)

EM allele at the E-locus introduces a black mask over the muzzle and sometimes ears.

• e/e + d/d + b/b = Platinum French Bulldog

K-Locus: Dominant Black and Brindle

• KB/ = Dominant black – suppresses A-locus expression

• ky/ky = A-locus is expressed (fawn, tan, sable)

• kbr/ = Brindle pattern expressed (requires ky)

Brindle French Bulldogs carry the kbr allele, and their base color (fawn, chocolate, blue) is overlaid with tiger-striping.

Example:

• ay/ay ky/ky kbr/kbr = Fawn Brindle

S-Locus: White Spotting – Piebald

This locus is responsible for the piebald pattern, or white spotting on the coat.

• S/S = Solid coat

• S/sp = Minor white spotting

• sp/sp = Full piebald (large white patches, often symmetrical)

Important: White markings are not pigment—they are the absence of pigment. Piebald Frenchies can be fawn, blue, chocolate, or lilac beneath the white spotting.

M-Locus: Merle Patterning

The M-locus causes patchy dilution (merling) in eumelanin. It is dominant:

• M/m = Merle

• m/m = Non-merle

• M/M = Double Merle, often associated with health problems (deafness, eye defects)

Merle French Bulldogs must NEVER be bred to another merle.Merle + dilution = blue merleMerle + chocolate = chocolate merleMerle + b/b d/d = lilac merle

H-Locus: Harlequin (Rare)

Though rare in French Bulldogs, harlequin modifies the merle pattern—turning gray areas to white and amplifying contrast. Requires both M and H alleles to express.

I-Locus: Intensity

Controls how rich red/yellow pigments appear.

• Intense (II or I/i) = Deep red/fawn

• Diluted (i/i) = Cream, pale yellow

🔬 Common and Rare French Bulldog Color Combinations

Color Name	Genotype
Fawn	ay/ay, ky/ky, E/E, D/D
Brindle	ay/ay, kbr/kbr, E/E
Cream	e/e, any K, any A
Blue (gray)	d/d, B/B, E/E
Chocolate	b/b, D/D, E/E
Lilac	b/b, d/d, E/E
Isabella	b/b, d/d, and possible intensity dilution
Platinum	e/e, d/d, b/b
Merle	M/m, any base color
Blue & Tan	at/at, ky/ky, d/d
Chocolate & Tan	at/at, ky/ky, b/b
Lilac & Tan	at/at, ky/ky, d/d, b/b
Piebald	sp/sp, any base color

🧪 Breeding Color Combinations

To produce:

• Lilac: Both parents must carry b and d alleles. (e.g., Chocolate + Blue)

• Isabella: Breed two lilacs that carry the intensity dilution

• Cream: Both parents must be e/e

• Merle: One parent must be M/m, and the other must be m/m (non-merle)

• Brindle: One parent must carry kbr

• Piebald: One or both must carry sp

⚠️ Health Considerations

• Merle x Merle = High risk: deafness, blindness

• Blue gene (d/d): may be linked with Color Dilution Alopecia (CDA)

• Cream and white coats: prone to sunburn and vision/hearing issues

Always DNA test breeding dogs before planning litters to avoid hidden double recessives or high-risk combinations.

🧬 Summary: Designing Your French Bulldog’s Coat

Producing a specific French Bulldog coat color requires DNA-level planning. Modern breeders often use genetic panels (like those from Animal Genetics) to determine the following:

• What genes a dog carries (visible and hidden traits)

• Which combinations will yield desired outcomes

• How to avoid genetic disorders tied to specific color genes

With responsible breeding and genetic testing, you can produce rare, healthy, and beautiful French Bulldogs in shades ranging from warm fawn to icy platinum.