A plain-language guide to French Bulldog color genetics
Every Frenchie coat is the result of a handful of genes working together. Once you understand French Bulldog color genetics, a DNA panel stops looking like code. This VerifiedStuds guide explains each locus, which colors can be tested, and what to ask before you choose a stud.
A locus is simply a place on a chromosome where a gene sits. Each dog has two copies of every gene, one from each parent. Therefore, a lab report shows two letters per locus.
Locus
What it controls
Common results
A (agouti)
Pattern of the base coat
ay fawn, at tan points
K
Brindle and solid black
kbr brindle, ky lets the A locus show
E
Cream and the dark mask
e/e cream, Em mask
D (dilute)
Turns black pigment blue
d/d blue
B and Co
Two different brown genes
b/b chocolate, co/co cocoa
S
White spotting
Pied pattern
M (merle)
Mottled patches
Not a traditional Frenchie color
L
Coat length
Two long-hair copies give a fluffy coat
Most genes in French Bulldog color genetics are recessive. As a result, a dog can carry a color without showing it, and two plain-looking parents can still surprise you.
First, the K locus decides whether a pattern shows at all. Brindle (kbr) lays dark stripes over the coat. However, a dog with two ky copies lets the A locus decide instead.
Next, the A locus sets the pattern. The ay version gives fawn. In contrast, two at copies give tan points, the marking seen on a black and tan dog.
Finally, the E locus can override both. Two copies of e hide all dark pigment, so the dog looks cream. The Em version adds the dark mask that many fawn Frenchies wear.
The D locus does not add a color. Instead, it thins the pigment. A black dog with two dilute copies (d/d) looks blue, and a fawn dog looks blue fawn.
Brown is more complicated in this breed, because Frenchies have two brown genes. The B locus gives the brown found in many breeds. Meanwhile, the Co locus gives cocoa, a darker brown first described in French Bulldogs. Before the cocoa test existed, breeders called it "non-testable chocolate".
When dilute combines with brown, the coat turns pale. For example, cocoa plus dilute gives lilac, while B locus brown plus dilute gives Isabella. See our page on blue and lilac French Bulldog studs for fees and what to check.
The AKC standard accepts white, cream and fawn, with brindle, piebald and mask markings. Blue, liver, black and tan, and merle are listed as disqualifications. Therefore, those dogs can be registered when their parents are, but they cannot be shown.
None of that makes a rare-colored dog unhealthy on its own. Still, it does mean the puppies are sold as pets. So an honest breeder says this plainly to every buyer.
Merle needs special care. One copy of the merle gene gives the mottled coat. However, a puppy with two copies, called a double merle, has a high risk of deafness and eye defects. For that reason, two merle dogs should never be bred together.
In addition, merle can hide. A cream dog (e/e) may carry merle without showing any patches. Because of this, a careful breeder runs an M locus test on both dogs before any breeding where merle might be present.
Coat length is separate from color. Two copies of a long-hair variant in the FGF5 gene give a fluffy coat, and one copy makes a carrier. In Frenchies, labs look for the L1 and L4 variants. Read more on our fluffy French Bulldog stud page.
Ask for the full panel. A proper report names the lab, the dog and the result at every locus, not just the color the owner is selling.
Check which variants were tested. For example, a long-hair test should cover both L1 and L4, and a brown test should cover B and Co.
Compare it with your female. Since most color genes are recessive, the puppies depend on what both parents carry.
Ask about merle. If either dog could carry it, both need an M locus result first.
Put health first. Color DNA does not replace hips, eyes, patellas, heart and a brucellosis test. See the French Bulldog health-testing guide.
Rare colors raise fees, sometimes sharply, which is why French Bulldog color genetics gets so much attention. Even so, a color panel is not a quality mark. A proven, healthy standard-color male is often the better choice for a first litter. Our stud fee guide explains how fees are set. When you are ready, find a health-tested stud or list your stud free.
Which French Bulldog colors can be DNA tested?
Nearly all of them. Labs test the A, K, E, D, B, Co, S, M and L loci, so a full panel shows what a dog carries as well as what he shows.
What is the difference between chocolate and cocoa?
They are two separate brown genes. Chocolate is tested at the B locus, while cocoa is tested at the Co locus. A dog can carry one or both.
Can two fawn Frenchies have a blue puppy?
Yes, if both parents carry one dilute copy. In that case, about one puppy in four will be dilute.
Why is breeding merle to merle dangerous?
Puppies with two merle copies often have hearing loss and eye defects. Therefore, responsible breeders never pair two merles.
Does coat color affect health?
Usually not. However, dilute dogs can develop color dilution alopecia, and double merles face serious risks.
Sources: UC Davis Veterinary Genetics Laboratory, dog coat color and merle tests, Paw Print Genetics, Co locus (cocoa), AKC French Bulldog breed standard.
Every profile shows color DNA and health results beside the fee.