You may have noticed that French Bulldogs come in a wide variety of colors and patterns. Where do these colors and patterns come from? Well, you have to know a little about genetics to fully understand.
Genetics 101
Dogs, just like humans, are diploid organisms. This means that they have two alleles at each genetic locus. A genetic locus is a position on a chromosome that contains a particular gene. In humans, one locus may contain the gene for hair color while another locus may contain the gene for eye color. However, each locus contains two alleles. One of these alleles comes from mom and one comes from dad. Mom and Dad each have two alleles for hair color and either one of these alleles have the potential to get transferred to their offspring. There are dominant alleles usually denoted with capital letters and recessive alleles usually denoted with lower case letters. For example, brown hair is dominant and blonde hair is recessive so the allele for brown hair would be denoted as “B” and the allele for blonde hair would be denoted as “b”. A person only needs one dominant allele for that trait to be expressed. However, they need both recessive alleles for the recessive trait to be expressed. When mom and dad pass on the hair color alleles to their offspring, there are three possibilities: BB, Bb, and bb. If the alleles passed on make the combination of BB (meaning both mom and dad passed on the brown hair gene) then brown hair will be expressed. The child will have brown hair. If the alleles passed on make the combination of Bb (meaning one parent passed on the brown allele and the other parent passed on the blonde allele) brown hair will also be expressed. This child will also have brown hair. If the alleles passed on by mom and dad make the combination of bb (meaning both mom and dad passed on blonde gene) the child will have blonde hair. The only way a recessive trait will be passed on is if both parents pass on their recessive allele for that gene.
Since dogs are diploid organisms like humans, the basic premise holds true for dogs and coat color. However, there are many loci for coat colors and patterns in a dogs genetic code. Additionally, there may be more than two possible alleles at each locus. Let’s go over each genetic loci and which combinations lead to which coat colors and patterns.
Genetic Loci for coat color in dogs
The A locus has three possible alleles: ay, at, and a. The “ay” allele is the allele for fawn or sable coloration. The “at” allele is the allele for black and tan coloration (this is where dogs get tan points). Since “ay” and “at” are dominant, dogs only need one copy of “ay” to be fawn or sable and only one copy of “at” to have tan points. Finally, the “a” allele is the allele for black coloration. However, having the “aa” allele combination doesn’t necessarily mean the dog is black. For example, a dog that is dd (Blue) at the D locus and aa (Black) at the A locus will still be blue. However, the “aa” allele combination will make for a more uniform blue coat color. This brings me to the next locus.
The D Locus is the diluted coat color locus. This is where we get the blue coat color from. The allele combination of “DD” simply means that the gene is not diluted. If this was the only locus in play, the dog would be black. The allele combination of “Dd” means that the dog is a carrier of the diluted gene and will not express the diluted color is most cases. The D locus must contain two copies of the d allele to express the blue color. Therefore, the “dd” allele combination will be blue. We get the lilac coloration from the dd / bb combination bringing me to the next locus.
The B locus is the locus for brown coloration or chocolate as we call it in the frenchie world. It has two possible alleles: B and b. Since chocolate coloration is recessive, you must have the two recessive alleles (bb) for the chocolate coloration to be expressed. The “BB” allele combination does not carry chocolate at all. The “Bb” allele combination is a chocolate carrier and could pass it’s recessive chocolate allele on to it’s offspring. However, in order for this offspring to have the chocolate coloration, the other parent must also pass on the recessive (b) allele.
The E locus is interesting because it contains the alleles for cream coloration and for the black masks. Because they are both on the same locus, a cream puppy can not also have a black mask. They can only have one or the other. Much like the blue and chocolate coloration, cream coloration is recessive so the puppy must have two recessive alleles (ee) to express the cream coloration. The allele for a black mask is Em which is dominant so a puppy only needs one copy of this allele to have a black mask. Note, however, black masks can be muted by dark coats. Another interesting fact about the E locus is that if you produce offspring with the double recessive allele (ee), the dog will show as cream even if it has the blue and chocolate allele combinations. Therefore, a dog with the allele combinations of “dd bb ee” will be cream colored. This is the combination that produces platinum puppies.
The K locus is mostly known for the brindle patterns in french bulldogs although it is actually called the dominant black locus. The allele for brindle patterning (Kbr) is a dominant gene. Therefore, a puppy with only one copy of the Kbr allele and having an allele combination such as “Kbr Ky” will show brindle patterning and of course the allele combination of “Kbr Kbr” will show brindle patterning. If the allele combination is showing no brindle (Ky/Ky), then the A locus, B locus, and D locus will determine the pattern on the coat.
The S locus is called the piebald locus and this is where our pied cuties get their patterns. The pied pattern is a recessive trait so a dog needs an allele combination of both recessive alleles (ss). An allele combination of “ns” will carry the pied pattern and can pass it on to it’s offspring. An allele combination of “nn” will not carry the pied pattern and can not pass the trait on since it does not have an allele for the trait.
The M locus is the merle locus and is another dominant gene. The two alleles for this locus are M (the dominant allele) and m (the recessive allele). For a puppy to be Merle, it must have an allele combination of “Mm” or “MM”. However, it is important to not breed puppies with the potential of carrying both dominant Merle alleles (MM) because a very high percentage of these puppies are deaf and/or blind.
Let’s put some of these combinations together to see what we have:
dd Bb atat kyky = Blue with tan points
Dd Bb ata kyky = Black with tan points
Dd Bb aa kyky = Black
Db Bb aa KbrKbr = Brindle
dd Bb aa KbrKbr = Blue Brindle
dd Bb aa kyky = Blue
dd Bb ayay kyky = Blue fawn
dd bb aa kyky = Lilac
There are many different combinations to obtain the many different variations in coat color and patterns we see in french bulldogs and there is much more complexity to the genetics than I have laid out in this post. What is important to remember is that to truly see what a dogs coat color and pattern will express, you must consider all loci together and understand how each affects the other. I hope this post at least gives you a starting point and a little glimpse into french bulldog colors and patterns and the genetics behind it.
If you wish to talk more about this subject or are still unsure as to which allele combination would show which colors and patterns, feel free to send me a message on my contact page.
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