Lesson 2- They’re all black or chocolate
In this lesson, we’re going to talk about one of the simplest of the color genes. The B locus that gives us black and chocolate (brown to the non-rabbit person but in rabbits a brown rabbit is called chocolate). I bet you didn’t know that EVERY rabbit is actually one of only two colors. They’re all either black or chocolate. I know that sounds crazy but trust me, it’s true. All of those other cool colors you’ve seen are just black or chocolate that’s being affected by other genes. They change the way the color looks but that’s all. You still have a rabbit that’s one of those two colors at its core.
Black is represented by a capital B and chocolate by a lowercase b. The reason for this is that black is the dominant allele at the B locus. Being dominant means a rabbit only needs one copy of B to be a black rabbit. In a rabbit’s genotype that can be written as 1- B_, 2- BB or 3- Bb depending on if the second allele is 1- unknown, 2- black or 3- chocolate. So how can I be sure that the rabbit who has Bb is black and not chocolate you ask? That’s because chocolate is recessive. For a recessive gene to show itself you need to have two copies of the gene OR, one copy along with an allele that is recessive to it. Since there is no allele that’s recessive to chocolate you have to have two copies in order to have a chocolate rabbit.
As you can see from the diagram, you must have two copies of the recessive b allele or you end up with a black rabbit.
Let’s step back for a second and consider how that would help you when looking at a rabbit you want to breed- Let’s take two pedigreed rabbits. Both of them are black but you would like to have some chocolate babies. Suppose for a second that both of your rabbits have a black father and a chocolate mother. Do you know what that means? It means that they both HAVE to be Bb in their genotype. Why, you ask? Because by being black we know they have B in their genotype but because their mother was chocolate the only thing she could have passed down to them was b. There is no other choice but for them to be Bb. That means that if you breed those two rabbits together you have a good chance of getting those chocolate babies you want. Let’s go back to those rabbits and say that they both have ALL black rabbits on their pedigree. That means they can only be BB right? Actually, because chocolate is recessive, and you need two copies for it to show in the color, the chocolate gene could be passed down for generations and nobody would know. Not until one of those chocolate carriers was bred to a chocolate or another chocolate carrier. There has been many a surprised breeder that found out a recessive gene had been hiding away in their rabbits! And do you know how many generations it could have been hiding? In theory, it could have been hiding for dozens upon dozens of generations!
And there you have the two colors that EVERY rabbit is. Dominant black and recessive chocolate. From now on, when you look at a rabbit you’ll know that they’re one of those two colors.
In the next chapter, we’ll cover some of the things that can make a rabbit, be it black or chocolate, look completely different. We’ll be looking at the A locus first and then moving on to D. I know, you’re wondering what happened to the C locus. Trust me, we’ll get there, but first we’re going to cover some of the easier, and more common, colors that you’ll be dealing with. The A locus will help you understand castor (called chestnut or agouti black among other names), and the other agouti colors, as well as self and otter, while the D locus will explain where blue, lilac, fawn, and all the other dilute colors come from.