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The Power Duo of French Bulldog Coat Colors: B‑Locus & D‑Locus

When breeders and enthusiasts talk about today's most popular and trendy French Bulldog colors—like blue, chocolate, lilac, and platinum—they’re referring to the powerful interaction between two key genetic loci:

  • B‑locus (TYRP1): Governs whether eumelanin pigment appears black or brown/chocolate,

  • D‑locus (MLPH): Controls dilution of pigment—turning black into blue, and brown into lilac or isabella.


These loci offer a genetic palette that drastically affects coat appearance, sometimes more than classic fawn, brindle, or piebald. Let's explore how each works, how they combine, and why breeders are so drawn to them.

french bulldog color dna

🧬 B‑Locus: The “Chocolate Gene” (TYRP1)

The B‑locus houses the TYRP1 gene, essential in synthesizing eumelanin (black pigment). Mutations here convert black into brown—known variably as liver or chocolate.

  • Alleles:

    • B (dominant): produces black pigment

    • b (recessive): produces brown/chocolate when homozygous b/b 

In breeds like French Bulldogs, there are multiple recessive b variants (e.g. b^s, b^d, b^c) . Yet in Frenchies there's also a special cocoa (co) mutation that causes a unique chocolate variant distinct from TYRP1; it's tested separately.

Key Points:

  • Only b/b (or co/co) dogs show brown hues.

  • Black-nosed dogs (B/_) stay black—even if they carry b.

  • In e/e (cream) dogs, b/b only affects nose/pads, not coat.


💧 D‑Locus: The Dilution Gene (MLPH)

The MLPH gene at the D‑locus influences how pigment is distributed in hair:

  • Alleles:

    • D (wild-type): full pigmentation

    • d (recessive): produces dilution when homozygous (d/d) 

There are multiple d mutations (d1, d2, d3); compound variants (d1/d2 etc.) also cause dilution .

Phenotypic Effects:

  • B/– with D/D = black coat

  • d/d transforms that black into blue (steel-grey) 

  • b/b with d/d = lilac or isabella depending on variant 

  • In e/e dogs, d/d gives champagne or pale cream 


🎨 Combining B & D: Trending Frenchie Colors

Here’s how combining B‑ and D‑locus genotypes produces colors breeders are favoring:

1. Blue French Bulldogs

  • Genotype: B/–, d/d, E/–

  • Appearance: Diluted black = slate/steel grey coat

  • Nose/Pads: Slate-blue

  • Breeder Benefit: Elegant grey tone, visually striking in photos

2. Chocolate French Bulldogs

  • Genotype: b/b (or co/co), D/–, E/–

  • Appearance: Warm brown tones; cocoa variant is deeper/warmer

  • Distinct: Chocolate is rich brown; cocoa can yield darker or milkier tones

3. Lilac / Isabella

  • Genotype: b/b (or co/co), d/d, E/–

  • Appearance: Light, pastel-toned coat—common names:

    • Lilac = chocolate + dilution

    • Isabella = brown + dilution variants

  • Appeal: Rare, pastel aesthetic; elevated by dilution

4. Platinum / Champagne Cream

  • Genotype: co/co, d/d, e/e

  • Appearance: Pale, pastel-coated platinum Frenchie—dramatic and unique 


📈 Why Breeders Favor These Colors

  1. Rarity & Value

    • Diluted or chocolate-based colors are uncommon—thus commanding premium prices.

  2. Visual Impact

    • Colors like blue and lilac photograph beautifully and stand out.

  3. Genetic Predictability

    • Both B and D mutations are recessive, enabling breeders to use DNA testing to predict litters with high precision.

  4. Brand Differentiation

    • Creating signature “lilac line” or “platinum litter” sets breeders apart in the market.


🧪 Breeding Strategy (Genetics Tips)

  • Blue from Two Carriers

    • Breed two B/–, D/d dogs → 25% chance of blue (B/, d/d).

  • Lilac Requires Stacking

    • Pair two chocolate carriers (b/b or co/co) that are both dilute (d/d) → all puppies will be diluted chocolaty tones.

  • Platinum is Triple Stack

    • Requires co/co + d/d + e/e → complete cream dilution; very rare.

  • Carrier Awareness

    • Dogs with one copy of b or d (B/b, D/d) look normal but carry hidden traits—DNA testing is key.


⚠️ Considerations & Risks

  • Health Risks:

    • Dilute coats may link to Color Dilution Alopecia, leading to skin issues.

  • Genetic Health Testing:

    • Essential to avoid harmful allele stacking—e.g., e/e (cream) dogs may have sun sensitivity.


🔍 Genetic Testing – Essential Tools

Top labs like Animal Genetics, Embark, and VGL offer:

  • B‑locus testing (detects b, co variants)

  • D‑locus multi-allele testing (d1, d2, d3)

  • Combined panels for breeders to strategize mating for targeted colors.


🧩 Visual Summary

| Genotype | Phenotype | Trend Factor || B/–, D/– | Black | Common || B/–, d/d | Blue | High || b/b, D/– | Chocolate | Popular || b/b, d/d | Lilac/Isabella | Very High – rare || co/co, d/d, e/e | Platinum | Ultra — extremely rare |


✅ Combination

The combination of B‑locus and D‑locus allows French Bulldog breeders to unlock a palette of eye-catching and commercially valuable coat colors—blue, chocolate, lilac, isabella, and platinum. With reliable DNA testing, breeders can predict outcomes precisely, creating “designer” litters that appeal to niche markets.


Yet, selecting for these traits requires ethical considerations—health testing, avoiding genetic disorders, and maintaining breed standards—to ensure that beauty doesn't come at the expense of wellbeing.



🧩 1. Punnett Squares: Visualizing B & D Locus Outcomes

A. B‑Locus (Black vs. Brown)

Parent genotypes: B/b × B/b yields:


B

b

B

BB (black)

Bb (black carrier)

b

Bb (black carrier)

bb (chocolate)

Phenotype probabilities per pup:

  • 75% black (BB or Bb)

  • 25% chocolate (bb) 

B. D‑Locus (Dilution)

Parent genotypes: D/d × D/d yields:


D

d

D

DD (non-dilute)

Dd (carrier)

d

Dd (carrier)

dd (dilute)

Phenotype probabilities:

  • 75% normal pigmentation (DD or Dd)

  • 25% dilute color (dd)

C. Combined B + D Loci

Pair parents B/b; D/d × B/b; D/d, Punnett grid (simplified):

  • Black: B/–; D/– → 56.25%

  • Blue: B/–; dd → 18.75%

  • Chocolate: bb; D/– → 18.75%

  • Lilac (or Isabella): bb; dd → 6.25%

Thus, each pup has a 1-in-16 chance of being lilac, making this color rare and highly coveted.


🎯 2. Breeding Strategies for Trend Colors

Blue French Bulldogs

  • Genotype target: B/–; d/d; E/–

  • Best achieved by pairing carriers: B/b; D/d

Chocolate

  • Genotype target: b/b; D/–

  • Simplest path: breed two:b carriers; both can be D carriers or non-carriers.

Lilac / Isabella

  • Genotype target: b/b; d/d; E/–

  • Rare due to stacking of two recessives; best achieved by breeding two fully dilute chocolates (bb dd).

Platinum

  • Genotype target: co/co; d/d; e/e

  • Extremely rare triple stack requires tests for the co (cocoa) locus and e/e cream gene in addition to b and d.


⚠️ 3. Color Dilution Alopecia (CDA): A Recessive Concern

Dilution (dd) predisposes dogs to Color Dilution Alopecia, a hereditary skin condition marked by follicular atrophy, hair loss, scaling, and potential secondary infections.

  • Symptoms typically appear between 6 months to 2 years.

  • Not all dilute Frenchies develop symptoms—some breeds tolerate dilution better (e.g., Weimaraner, Great Dane).

  • Management includes shampoos, fatty acid supplementation, antibiotics for infections, but no cure.

  • Ethical breeding suggests excluding dd dogs from future matings.


🧩 4. Breeding Decision Flowcharts & Pedigree Strategies

Breeding Flow Example: Lilac

  1. Screen prospective parents with full B, D, E, and co tests.

  2. Choose bb dd carriers (chocolate or dilute chocolate).

  3. Breed carrier × carrier → ~6.25% lilac pups; rest distributed among blue, chocolate, black.

  4. Genotype each pup; only keep healthy carriers, ethically removing dd from breeding rotation.

Pedigree Integration

Document each dog's:

  • Genotypes: B/B, B/b, b/b; D/D, D/d, d/d; E/E, E/e, e/e; co/co

  • Phenotypes and any CDA signs

  • Test results for transparency across generations


📊 5. Summary Table: Genotype to Phenotype

Phenotype

Genotype

Breeding Requirement

Dilution Risk

Black

B/–; D/–

Common

None

Blue

B/–; d/d

Breed two carriers

CDA risk

Chocolate

b/b; D/–

Breed carriers

Low

Lilac

b/b; d/d

Two dilute chocolates

High CDA

Isabella

b/b; d/d; intensity variants

Breed dilute chocolates with cream influence

High

Platinum

co/co; d/d; e/e

Rare triple stack

High

✅ Final Notes

  • DNA testing is non-negotiable—especially for breeding dilute colors.

  • Ethically avoid breeding dd dogs to dd or even Dd carriers to reduce CDA.

  • Use Punnett squares and calculators (e.g., Sage Coat Colour Calculator) to model outcomes.

  • Document genetic health and genotype data in pedigrees.

  • Balance aesthetic goals with canine wellbeing—never compromise health for color.


By including clear visual genetics, breeding guidance, and responsible health considerations, this section will offer French Bulldog enthusiasts and breeders a scientifically solid, data-driven reference—empowering informed decisions in both aesthetics and wellbeing.


Chino, D. (2025). The Genetic Blueprint of French Bulldog Coat Colors: A Deep Dive into B‑Locus and D‑Locus Combinations. Written by Don Chino, Harvard Animal Scientist and internationally recognized as the Best French Bulldog Breeder by the AKC, UKC, and DKC.

 
 
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