Brindle & Red Dog Genetics

After alot of research and reading several different opinions I think I will put together how I think the dog genetics work.

According to one theory the E locus is the locus that the black mask, brindle, and red genes are located on. Following is a list of the genes in order of dominance.

E(m) - Black Mask gene. This gene makes the black mask (and ears) that is seen in bullmastiffs.

E - Dark color gene.

e(br) - Brindle gene. This gene makes the brindle pattern/color.

There is one more gene in the E series but it appears that it is not in Bullmastiffs.

According to this theory it is believed that a brindle’s genotype is: E(m)e(br). According to this theory if you breed a brindle to a brindle you have a 25% chance of getting brindles with out black masks (ebrebr), 50% chance of getting brindles with a black mask (Emebr), and 25% chance of getting reds/fawns (EmEm). According to this theory the reds/fawns genotype is EmEm which cannot always be true. What if you breed 2 brindles who both have a black mask together and you get some red/fawn offspring that DO NOT have a black mask. Then where does that fit in. Those reds/fawns who do not have a black mask cannot have the genotype EmEm since they do not have black masks. They would have to be EE in order to be reds/fawns with out a black mask. Reds/fawns are either EmEm or EmE. Most of the time they are EmE, as with the E present, alot of the time those dogs would not have masks. The E series is all on one locus. Genetically speaking it is a known fact that there can only be 2 genes on one locus therefore, a dog can only have 2 genes on one locus. The dog’s genetic combination would have to be one of the following: EmE, Emebr, EmEm, Eebr, EE, or ebrebr. All of the genetic combinations that do not have the black mask gene will not have black masks. Thus according to this theory a brindle dog that has a black mask would be Emebr. If it was bred to another black masked brindle then it COULD NOT produce any reds without black masks (since the red HAS to have one E gene to be a red without a black mask). 2 dogs with black masks CAN produce dogs without black masks. From all that I have researched it appears that the brindle gene is NOT on the E locus. Instead the E locus only includes: Em, and E. The brindle gene is on a separate locus - the K locus.

The genes on the K locus are as follows. They are in order of dominance:

k(br) - Brindle

k - non-brindle.

There is one more gene on the K locus (it is K, the most dominant gene). But, it appears it is not in Bullmastiffs.

According to this theory a brindle with a black mask would be, EmE kbrk. If it was bred to another brindle with a black mask who had the same genotype as the brindle above (EmE kbrk) it could produce 75% black mask puppies and 25% non black mask puppies. It could also produce 75% brindle puppies and 25% non-brindle puppies (reds or fawns). This gene series makes much more sense than the E series.

I believe the brindle gene is not on the E locus but is on the K locus. It makes it much easier to figure out the genetics of 2 brindles. It also shows that 2 brindles bred together CAN produce non-brindles. Here is an example:

I know of a recent breeding where a red brindle black masked female (out of a red x brindle breeding) was bred to another red brindle black masked male (also out of a red x brindle breeding). The puppies they produced were 1 red, and 10 brindles. If the brindle gene was on the E locus it would be IMPOSSIBLE to get ANY reds. If the brindle gene was on the E locus the brindle’s genetics would be Emebr. The only colors that could be produced out of that breeding would be brindles. That is not true. When 2 brindles are bred together reds CAN be produced. Since the brindle gene is on a separate locus (K locus) the 2 brindles genetics would be EmE kbrk, thus they could produce the red that they did.

In conclusion it appears that in Bullmastiffs we are working with 4 genes. E(m) for the black mask and ears, E for dark color, k(br) for brindle, k for non-brindle.

**NOTE** These genetics work for any breed but, I was focusing in on the Bullmastiff Breed.