Rabbit Coat Color Genetics Made Easy: Part 1 Your Rabbit’s Base Color

When I first started breeding rabbits I spent so many evenings reading  different explanations of how rabbit colors interact with one another, that my head would spin. And just as I thought I had finally ‘got it’ another color option would spring up to confuse me.  

Despite my background in science, I found the whole subject a little confusing. What helped me was focusing on one part of the rabbit color code at a time. 

I’ll explain what I mean, and why I chose this approach. And I’ll also explain some of the terminology of color genetics so that it is easier to follow. I think you’ll find its actually fun when we do it like this. 

The ABC of rabbit color

There are five main genes controlling rabbit coat color and they are conveniently labelled for the first five letters of the alphabet.  ABCDE  So far so good!  

But the first obstacle to understanding rabbit genetics is that these letters aren’t actually genes. The letters represent the location of genes, not the genes themselves.  Scientists call each of these locations a ‘locus’.  

So we have the A locus, the B locus,  the C locus etc. And at each locus there are two alternative versions of the gene that lives there. We call these versions alleles. Don’t worry, we’re going to explain these terms. And figure out how they can help us understand rabbit coat color. 

Genetic jargon

Here are three genetic terms that you need to be clear on.

• Locus
• Gene
• Allele

The locus is where genes live. People often use gene and allele interchangeably. But gene is a broad term for the coding that makes things happen. And alleles are variations of each gene. Let’s go in a bit closer.

What is a gene? 

Genes contain the code for each of the characteristics that go to create the animals we know and love. 

So we have genes that contain the code for coat color. And other genes that contain the code for coat pattern. And yet more genes that contain the code that decides how intense the color is. So for example whether black fur is a rich dark black, or a pale bluey grey. 

Then there are genes for eye color, coat length, coat texture, and more. But we are going to be concerned today with just those genes that affect fur color and the way that color is distributed across the rabbit. 

We’ve seen that each gene has a ‘locus’ or place where it can reliably be found.The gene that decides rabbit coat color for example, lives at the B locus. And we are going to focus mainly on this B locus to begin with. 

Genes are strung together along a chromosome, like beads on a necklace. Rabbits have 22 matching pairs of chromosomes, 44 in all. One of each pair inherited from the mother rabbit and one of each pair inherited from the father. 

Location Location

At any locus, there are two versions of the gene, alleles, that live there. If a chromosome was a street, the alleles would be a bit like two houses exactly opposite each other, either side of that street. 

Each allele at the same locus contains a set of instructions for a single attribute of the rabbit. So at the A locus, we have instructions for coat patterns. And at the B locus we have instructions for coat colors.  

There are two versions of the gene because one allele comes from each of the rabbit’s two parents. 

When Alleles Match

Sometimes the two alleles are identical. So for example a black rabbit might have two alleles for black fur. 

We use the same letter as the locus to represent the alleles (one from each parent)  So a black rabbit that inherited the black fur allele from each parent would be represented by the letters BB

To help us recognize which allele we are looking at we use a lowercase letter for the other allele. So a brown rabbit that inherits the brown fur allele from each parent would be represented by the letters bb

When Alleles Don’t Match

But what happens when the rabbit inherits a black fur allele from one parent and a brown fur allele from the other parent? 

We’d represent this with the letters Bb. And the rabbit would have black fur not brown. 

That’s because black fur is dominant over brown fur. The capitalization of the letters (or lack of it) shows you whether or not that allele is dominant (uppercase) or recessive (lowercase)

But what does dominance mean? And why does your Bb rabbit look black rather than a mixture of black and brown?

What Is A Dominant Allele? 

When one allele is dominant, this means it has the power to switch off the other allele. This is the case with black and brown (usually referred to as chocolate) fur.  

The rabbit that inherits the brown gene cannot be brown if there is a black gene present. It can only be black because black is dominant and prevents the brown gene from sending out its instructions. 

So a rabbit can only be chocolate colored if it inherits a brown fur allele from both parents. We’ll talk about this a bit more in a minute. 

The A Locus And Multiple Alleles

Sometimes there are more than two possible sets of instructions for a particular locus. The rabbit can only inherit two alternatives, one from each parent. But there can be more than two alternatives that exist within the breed.

This complicates matters.

And it happens with the A locus. I think a lot of confusion arises about this. Because there are three alleles that could potentially live at the A locus, even though only two can occur in any one rabbit (one from each parent) 

And that’s one of the reasons that I like to start rabbit coat color genetics by looking at the B locus. Which has only two variations. Followed by the D locus which also has only two variations. 

I think you’ll find that if you get your head around these two first, it will all seem much clearer. So let’s do that. We’ll catch up with A later. 

The B Locus – Your Rabbit’s Base Color

We’ve already started to get to know what the B locus does. It is responsible for the base color of your rabbit. And there are only two alleles, or variations, of that gene.

“But, but..!” you cry.  “If that’s the case, Pippa, why aren’t all rabbits either chocolate or black?”  

And that’s a very good point.

Clearly rabbits come in a dazzling array of color variations. How can those colors possibly come from just brown and black?

To understand that we need to look at the way the brown and black pigment can be diluted, at the pigments that exist within rabbit fur, and at the ways color can be distributed along a single hair shaft, or in patches around the rabbits body. Or even overwritten completely. 

I’ll keep it simple, I promise! Let’s look at the dilution factor first. 

The D Locus – Making Colors Dilute

Just like the B locus, there are two alleles at the D locus.  

The dominant D allele gives dense or full strength color.  So a DD rabbit will have a dense black or brown base color. 

The recessive d allele give instructions for dilute color.  So a DD black rabbit will be black and a dd dilute black rabbit will be a blue-grey color. We usually call this ‘blue’ but it is really a shade of grey. 

And what happens if the black rabbit inherits a D allele from one parent and a d allele from the other?  I’m sure you have guessed it. The Dd black rabbit will still be black. Because the dominant D allele switches off the ability of the recessive d allele to carry out its instructions. 

The situation is the same for chocolate rabbits but of course chocolate looks different from black when its diluted.  The dilute brown color is a pinky grey and we usually refer to this as lilac. 

So when it comes to solid colored rabbits, we now have four possible colors. 

• Black
• Blue
• Chocolate
• Lilac

Genotype Vs Phenotype

There’s another couple of useful genetic terms we can use at this point, and that’s genotype and phenotype.

Genotype refers to those alleles that we have been talking about. We use the letters of the alleles to write it down.  And phenotype refers to what the rabbit looks like.  

We always know the phenotype. It’s right there in front of us. But genotype can sometimes be difficult to figure out. 

Here’s our example from above, with the genotypes grouped by the phenotype of the rabbit

Phenotype = black

• BB DD
• Bb DD
• BB Dd
• Bb Dd

Phenotype = blue

• BB dd
• Bb dd

Phenotype = chocolate

• bb DD
• bb Dd

Phenotype = lilac

• bb dd

As you can see, we could have four black rabbits that look identical, yet each have a different genotype. There are fewer ways to be blue or brown. And if we have a lilac rabbit in front of us we know exactly what the genotype is. 

A Base On Which To Build

So all rabbits are basically brown or black. Think of this base layer as an undercoat that can be painted over, but is still there underneath even if we can’t see it. Even in a pure white rabbit.

The base colors of black and brown are created from a pigment called eumelanin.  It’s the same pigment that underlies coat color in most mammals. 

But there’s also a red toned pigment called pheomelanin which helps to create the huge variety in color that we see in rabbits. This red pigment is present in many of the patterns we see in rabbit coats and its distribution is controlled by a number of genes. It’s also influenced by the dilute alleles on the D locus. We’ll look at the genes that control the distribution of red pigment later on.  

For now, understanding these four base colors first will help us as we go forwards because they are present in all rabbits, even when they are masked or broken up by other genes. And they change the appearance of the coat patterns found in our different rabbit breeds. 

Check back soon for part 2!