Rabbit Coat Color Genetics Gene B

The "B" color gene is pretty straightforward and easy to understand, especially compared to the "C" gene, or even the "A" or "E" color genes.  That's because it comes in only two varieties:  the dominant "B" and the recessive "b." "Easy" is relative, when it comes to genetics!  But let's just dive right in.

Any Holland Lop you see either belongs to the black family of colors or the brown (chocolate) family of colors--regardless of the main color that you see when you look at the rabbit.  The vast majority of Holland Lops you will see at a show or at the typical barn belongs to the black family.  Black family colors include black (I bet you weren't surprised by that one!), blue, black tortoiseshell (tort), blue tortoiseshell, sable point, ermine and chinchilla.  Chocolate family rabbits include chocolate, lilac, and lynx, among others.

What's Going On Genetically

Black family rabbits are either "BB" or "Bb."  Unless you see a chocolate color in a rabbit's pedigree, it's fairly safe to assume it is "BB."  Chocolate family rabbits are always "bb."  And chocolate family rabbits cannot carry the black gene "B."  That's it.  All Holland Lops are either "BB," "Bb", or "bb."

What Happens When You Breed

When you breed a true-breeding black family rabbit, that is, a black with two dominant "B" genes, to another true-breeding black family rabbit, you will always get a true-breeding black family rabbit.  Another way to say that is that "BB" x "BB" always yields a "BB."  Each parent has only the dominant "B" to give its offspring.

When you breed a chocolate family rabbit to another chocolate family rabbit, we have the similar situation.  The parents have only "b" to give to the offspring, who are all "bb."  Thus "bb" x "bb" yields "bb."

Things get a little more interesting when you breed a true-breeding black family rabbit with a chocolate family rabbit, such as when breeding a black tortoiseshell to a lilac.  One hundred percent of the offspring will be black family rabbits that carry the chocolate gene.  Look at the chart below to see just how that happens. 

[Please note that the example above includes what happens when you breed a chocolate with a black tortoiseshell, such as when you are trying to improve the type of the chocolate family rabbits.  (The Holland Lops that conform most closely with standards are most often black tortoiseshell, thus they are often used to help improve the type of other-colored rabbits.)]

Now let's look at the result from breeding back one of these "Bb" offspring to another chocolate family rabbit (bb).  When you are breeding chocolates with your black tortoiseshells to improve type, you will readily see that it is a two-generation process.  In this second generation (breeding the offspring back to the chocolate parent, for example), two out of four offspring, on the average, will be chocolate, and the remaining two will carry chocolate.  Let's see how this works.

A lilac tortoiseshell might be a very handy rabbit to have when attempting to produce a specific full color chocolate family rabbit (full color means has a dominant color or "C" gene).  Since the genotype is aa bb C- dd ee, it would allow any recessive genes of the other parent to be expressed.

Conclusion

The black-chocolate color genes are very straightforward.  There are only three combinations ("BB," "Bb," and "bb").  Understanding what the chances are for producing chocolates when breeding different rabbits can help in your breeding plan, especially if you are breeding again to black tortoiseshells to improve type.  There is a corresponding color in the chocolate family for each color in the black color family.