Coat Color Inheritance in Boxers

An Overview of Boxer Coat Colors & Patterns

How many different terms have you seen when it comes to the colors of a Boxer? Fawn, brindle, flashy, masked, seal, reverse…there’s a lot going on. The coat colors of Boxers are very interesting to explore, and the genetics behind them are even more so. Let’s dive into the variations you’ll find and how they come about!

*Non-standard colors or terms like “black”, “reverse brindle”, “seal”, etc. will not be covered in this initial post. That’s down the road! 🙂

*This is a lengthy and informative post, so feel free to use these buttons to skip around!

Did you know that there are only two colors in Boxers?

You have a fawn coat, and you have a brindle coat. That’s it. Fawn is a shade of light brown which ranges from soft tan to a reddish or yellowish-brown. Brindle is described as vertical strips on the coat that show a change in texture and may show a change in pigmentation, or more simply, tiger-striped. Pictured above you have a brindle on the left and a fawn on the right. A brindle coat is actually the result of a black striped pattern on top of a fawn background.

Quick Rundown & Vocabulary:

Before we jump into this, let’s go over just a couple of terms that will need to be understood—

• Chromosome: a structure found inside the nucleus of a cell
• Gene: the basic unit of heredity passed from parent to offspring
• Locus: the physical site or location of a specific gene on a chromosome
• Allele: one of a pair of genes (one from mother, and one from father) at a specific genomic location (locus on a chromosome)

Basically, chromosomes carry our DNA in our cells in the form of genes. Each gene (typically) comes in pairs and is inherited as a distinct unit or allele. The locus is the physical spot on the chromosome in which a gene is located.

• Genotype: the genetic makeup of a cell
• Phenotype: the observable trait of genetic makeup

Basically, a genotype will refer to actual genes and alleles on paper, and a phenotype will refer to what that looks like in real life being expressed in the organism.

• Heterozygous: having two different alleles of a particular gene from each parent
• Homozygous: having two identical alleles of a particular gene from each parent
• Dominant: an allele that will be expressed over another with as little as one copy
• Recessive: an allele that will not be expressed unless an individual receives two copies

Basically, individuals receive two versions of each gene (alleles)..one from each parent. If an individual receives identical copies from both parents, they have a homozygous genotype for that gene. If they receive two different alleles from their parents, they have a heterozygous genotype for that gene. If an allele is dominant, an organism will express that trait receiving just one, or two copies. If an allele is recessive, an organism will only express that trait if it receives two identical copies of that allele.

Punnett Squares & Probability:

A Punnett square is a diagram used to predict the genotypes/phenotypes of a breeding and the probability of an offspring having particular traits. It’s named after Reginald C. Punnett who invented it in 1905, and the simplest version of this is the monohybrid cross. With “mono” meaning “one”, this cross is the examination of a single trait and gene.

We’ll recap using this example from Biology LibreTexts, so hopefully, the examples in Boxers make a little more sense. This example is for color in flowers. There are two colors, purple (which is represented by “B”) and white (which is represented by “b”). Both parents are represented on the top and left-hand sides. Both parent flowers have a heterozygous genotype of “Bb”. Both parent flowers appear purple, as the purple color or “B” allele is dominant over the recessive white “b” allele. The organism only needs at least one “B” allele to have the phenotype, or physical appearance, of purple.

If you cross them, starting in the upper left-hand corner you end up with BB, Bb, Bb, and bb. That makes 25% of the genotype BB, 50% it Bb, and 25% bb. That means that 75% of the phenotype is purple, while 25% of it’s white. The BB offspring have a homozygous genotype for purple, the Bb offspring have a heterozygous genotype for purple, and the bb offspring have a homozygous genotype for white.

*Keep in mind and note that these Punnett squares follow basic laws of probability. If there are four offspring, it is not set in stone that three flowers will be purple and one will be white. Each offspring will have these same odds separately. Think of it as rolling a die. There is an equal 1 out of 6 chance that you will roll a 1, 2, 3, 4, 5, or 6. But if you roll 6 times, it doesn’t automatically mean you roll one of each. You could roll three 4’s and three 2s. You could roll six 6’s. It’s a game of chance!

How does this tie into Boxers?

As mentioned, Boxers have two coat colors: fawn and brindle. The brindle stripes, or lack of, are controlled by the K-Locus or “Dominant Black” gene. There are actually thought to be three alleles, or variants, associated with this gene. There is K^B, which stands for “dominant black”, K^br which stands for “brindling”, and K^y which is a lack of black. K^B is not naturally present in the Boxer breed, so don’t worry about that. We’re trying to cover the basic coat colors here.

K^br is dominant to K^y, so if a Boxer receives even one copy of the K^br allele, it will have brindling! K^y is a recessive allele, which means a dog must receive two copies of this allele for it to be expressed. Since K^y is the lack of black, the expression of this gene is actually allowing the underlying color (fawn in the Boxer’s case) to be expressed.

So on a genotype-level your Boxer can be K^brK^br, K^brK^y, or K^yK^y. Phenotypically, or what this looks like physically, both K^brK^br and K^brK^y will result in a brindle pattern, whereas K^yK^y will let your dog’s fawn coat shine through. Making sense?

If you have a brindle dog, you won’t know if it’s K^brK^br or K^brK^y by looking at it since a dog only needs one copy of brindle for it to be expressed. You’ll either need a genetic test, or will find out by trial and error in breeding (obviously not recommended solely for experimenting) to confirm. I use embark for our dogs, because it tests for a number of things!

Coat Color Combinations in Boxers

Here’s where you’ll learn about how fawn & brindle puppies come about! Have you wondered what color puppies your brindle dog will produce? Have you wondered if a brindle Boxer can have fawn puppies? What about white dogs? Flashy?

Below I’ll list all the possible fawn and brindle crosses and combinations. We’ll go over the white after.

White Boxers

Did you know white Boxers don’t have a white coat? The white coloring in Boxers is actually caused by a separate gene, known as the “Spotting” gene located at the S-Locus. So white Boxers are really fawn or brindle underneath, with an overwhelming amount of white spotting! Flashy Boxers have white patches caused by the same gene, just in different locations and much less. (Flashy is just a term for white on Boxers. The more white on your Boxer’s face, neck, shoulders…the more “flash” it has.)

At the S-Locus there are two known alleles, or variants, associated with this gene. There is S, which stands for “solid/no white spotting”, and S^p which stands for “piebald”. Some sources cite a third and even fourth allele (Sⁱ allele which is “Irish spotting” and S^w allele which is “extreme white” or “extreme piebald”) but these aren’t agreed upon nor proven yet.

The S-Locus has alleles which are examples of incomplete dominance. What this means is rather than one allele being completely dominant over the other and masking it, both alleles are able to be partially expressed. On the genotype-level your Boxer can be SS, SS^p, or S^pS^p. Phenotypically, or what this looks like physically, is SS will result in plain/classic/non-flashy Boxer, SS^p will result in a flashy Boxer, and S^pS^p will result in a white Boxer. Keep in mind that 1) white boxers can still have small patches of fawn or brindle that aren’t covered by their white spotting and 2) even Boxers that are “plain” can still have very small patches of white.

The inheritance pattern works the same way as the K-Locus, so you’ll see the same examples of different parents’ crosses below! I did not include white x white, as it is not recommended to breed this cross due to potential health risks. Just know that this will cross the same way as 100% plain. White x white = 100% SpSp genotypically and 100% white phenotypically.

WRAPPING IT UP!

I hope this helps answer some questions you may have about coat colors, as well as the genetics behind them. Coat color genetics is a vast and ongoing subject of research, so there is so much more to learn as well as so much that has not been discovered. Genetics is like the ocean… we’ve only just scratched the surface!

I can’t wait to explore more, learn new things, and keep up with the current discoveries in the coat color world. There’s something new every day. Keep an eye out for upcoming deep dives into specific coats like the mystery of “sealed” Boxers, the intricacies of brindle, and much more. Thanks for jumping into the genetic rabbit hole with me!

– The Boxer Babe