standard rex rabbit genetics Standard Rex Rabbit genetics
Rabbit genetics
If you don't know where you are going and how to get there you are in for a long drive!

Scope: The scope of this report will be limited to the color genetics of the rex rabbit.

Purpose: The purpose of this report is to make the color genetics of the standard rex rabbit as easy to understand as possible. If you are in 4-H or just beginning to breed rex rabbits you are at the right place. 

Credentials: I have no background in rabbit genetics or biology. I have a BA Degree in Philosophy, a small hobby farm housing aproximately 75 rex rabbits and way to much time on my hands. Don't expect this report to get too deep :)

Feedback: Please e-mail me with any suggestions that may make this report easier to understand, and/or any corrections that need to be made.

Part 1. The canvas and the paint

There are 4 different types of rabbit fur according to ARBA (American Rabbit Breeder's Association, Inc.) normal, satin, wool, and rex. The focus of this text will be on the rex rabbit fur. However, the same genetics apply to the other fur types as well.

Normal fur: About 90 percent of rabbit varieties have normal fur. Normal fur is course to the touch due to 'guard hairs' that are longer than the shaft hair. It offers some resistance when stroked backwards.

Satin: Fine, dense fur, about 1 inch long, that has a clarity to the hair shaft that allows the pigment to shine through giving it a satin sheen to the appearance. Only the Satin varity of rabbit has this fur type.

Wool: From short and coarse to long and silky, the fur on the wool varieties of rabbit resemble the wool of a llama or alpaca.

Rex: Rex fur is only found in the standard rex and mini rex. It is short, about 1/2 to 7/8 inches in length, creating a dark rich color.  The guard hairs are shorter than the shaft hairs giving the fur the feel of velvet.

It is important to understand the way a rabbits' hairshaft gets its color. In rabbits each hair shaft gets the same amount of pigment to color it. This means that a short hair shaft will be a dark, rich color due to the concentration of the color into a smaller area while a long hair shaft will be a light, subtle color as a result of the color being 'stretched' to encompass the larger area. We can use mixing paints as an analogy. Imagine taking a cup of red pigment and mixing it into 1 gallon of white paint. We might expect to get a rich red paint as a result. Now imagine mixing that same cup of red pigment with 100 gallons of  white paint. We used the same amount of pigment, but now we get pink paint instead of red paint.

The pigment that colors a rabbits' fur comes in two colors black (some call this color dark brown) and yellow. All of the colors that we see in a rabbits' fur is a genetic manipulation of these two pigments. However, the yellow pigment can be made orange to even red in some cases with the addition of 'rufus modifiers'. More on modeifiers later.

Part 2. You got your mothers eyes and your dads nose, but your sister got your dads eyes and your mothers nose?? WHY!

When we breed rex rabbits (or anything for that matter), the resulting babies inherit characteristics from both mom and dad sent in the form of genes. However, these genes do not simply blend together. For example, a black buck and a white doe don't produce grey babies. I might get black babies, white babies or any number of other colors from the offspring. Why, and how, this is happening is what the rabbit breeder needs to know. The answer turns out to be simpler than you might expect. Lets get started with the explanation.

Genes: Every characteristic that makes a rabbit is made up of genes passed on from the buck and the doe to the baby. The baby recieves two genes for each characteristic. One from each parent. These genes come in three types; dominate, intermediate and recessive.  A dominate gene will always show itself and hide any intermediate or recessive genes. An intermediate gene will not show itself in the presence of a dominate gene, but will always show itself and hide any recessive genes. A recessive gene will only show itself in the presence of another recessive gene. Remember, our baby rabbit has two genes for each characteristic... one from each parent...  BUT we can see only one of these genes. The other gene is a secret, hidden from us by the most dominate gene, but it's still there.  Basically, we only ever see 1/2 of the rabbits' characteristics.  The other half is hidden. However, you can easily discover the 'secret' half of your rabbit through understanding how genetics work and keeping very good records of the rabbits parents and offspring. That is why it's so very important to keep accurate pedigrees of your breeding stock and litter records.

Characteristics: Scientists have taken groups of genes that determine things like eye color, fur type, fur color, etc. and have divided them into 'Series' assigning each a letter to identify them.  For example,  the 'color' gene has been assigned the series letter 'B'.  The dominate gene in the series is assigned a single, capital letter to designate it. In this case, a capital "B" which stands for Black. The most recessive gene in the series is designated by a single, lower case letter. In this case, a lower case "b" which stands for Brown.  Intermediate genes are given multiple letter desigations in lower case that begin with the series letter. You will understand this better as you read further below.

Lets look at our first characteristic and put it to use.

The "A" series of genes determines if your rex rabbit will be an agouti, an otter or a self.  There are three genes in this series.

AAgouti (dominate gene)     Causes the hair shaft to have 3 or more distinct bands of color with the exception of the bottom of the feet, inside of the ears, rings around the eyes, a triangular shape at the nape (back) of the neck and the underbelly.  These exceptions will be colored white, tan or fawn.

atOtter (also known as the tan gene)  (intermediate gene)    Same marking as an agouti except the hair shaft on the main body is a solid color.

a Self  (recessive gene)    The hair shaft is a solid color. 

Lets look at some photos and few examples of how to apply these genes to a breeding program.

Photo set #1 Agouti













Photo set #2 Otter












Photo set #3 Self













Example #1:

Let's say I have a standard rex buck named Hank who is an agouti. I did not get a pedigree when I purchased this rabbit, and don't know who his parents are. I have one other problem. I only raise and show self colored rex rabbits. What was I thinking when I brought Hank home?  Well, I was thinking Hank was one nice rabbit.  What a stud!  He has a solid front end, awesome depth and great fur. He would be the best rabbit in the barn if he was only a self.

Hank has two "A" series genes.  One he got from his mother and one he got from his father. Because he is an agouti, we know one of these genes has to be an A (Aguoti) but without a pedigree we can only guess at the other "A" series gene.   Because the "A" series gene that we see in Hank is the most dominate gene available, it could be paired up with another dominate A (Agouti) gene OR either the intermediate at (Otter) gene OR the recessive a (Self) gene.  Therefore, there are three possible "A" series gene makups that Hank could have.

1 - AA   Hank might have two dominate agouti genes
2 - Aat  Hank might have an otter gene that is hidden by the dominate agouti gene
3 - Aa   Hank might have a self gene that is hidden by the dominate agouti gene

I'm not going to let Hank just sit in the barn. He is just too nice a rabbit for that. I decide to breed him with my big self colored doe named Lucky. After all, I may need a little luck if I'm going to get a self colored baby out of Hank.

Lucky has two "A" series genes.  One from her mother and one from her father. We know that one of these genes is a (self), after all, we can see it on the rabbit.  Let's think about what we have learned.  We know the self gene is the most recessive "A" Series gene.  In order for us to see it, nothing can be 'hiding' it. Therefore, the second gene must also be a self because if it was an agouti or otter gene they would hide our self gene on the rabbit. The rule is, if we can see a recessive characteristic on the rabbit, we know that both genes MUST be recessive genes.


Because we are not sure what that hidden gene in Hank is, we have 3 possible outcomes when we breed Hank and Lucky.   Lets look at each possibility.

1 - Possibility one is Hank has AA genes.  We know Lucky has aa genes.

Now lets look at Image G-1. Hanks' dominate AA genes are charted at the left.
Luckys' recessive aa genes are charted at the top. The red, green, yellow and blue
squares show the 4 possible outcomes. Each box gets one gene from each parent.
Notice that all of the babies will have the same "A" series make up of "Aa". 
Hank can only pass on an A gene and Lucky can only pass on an a gene. 
All of the babies will be Agouti but they will have a hidden, recessive self gene from
their mother (Aa).




2 - Possibility two is Hank has Aat genes.   We know Lucky has aa genes.

Now lets look at Image G-2. Hanks' Aat genes are charted at the left.
Luckys' recessive aa genes are charted at the top. The red, green, yellow and blue
squares show the 4 possible outcomes. Remember, each box gets one gene from
each parent. Notice that this time only the red and green square babies have the
Aa make up. The yellow and blue square babies got the hidden otter gene from their dad.
We now know the odds are that 50% of the babies will be Agouti with a hidden self gene (Aa),
and 50% of the babies will be otter with a hidden, self gene (ata).




3 - Possibility three is Hank has Aa genes.  We know Lucky has aa genes.

Now lets look at Image G-3. Hanks' Aa genes are charted at the left
Luckys' recessive aa genes are charted at the top. The red, green, yellow and blue
squares show the 4 possible outcomes. Again the red and green square babies have
the Aa make up. The yellow and blue square babies got the hidden, self gene from
their dad... and we could not be more excited!  We now know the odds are that 50%
of the babies will be Agouti with a hidden, self gene (Aa), and 50% of the babies will be
self (aa).


It's been 31 days since I breed Lucky to Hank. Lucky has been pulling fur for two days now and I think today will be the day.  As I check the nest box, I feel my first warm, wiggly baby. I can't wait to check him out. When I'm done, I count eight babies. It will be another 7 to 10 days before I can tell what color they are.

It's day 10 and its clear that I have all agouti babies. I breed and show selfs, and now I have 9 agouti rabbits to cage and feed. Nothing to show for all my efforts. Now, what to do with Hank and the babies. I have a few choices. I could breed Hank again, and hope it was just bad luck that I got all Agouti. If Hank had any tan or self recessive genes, there would have been a 50-50 chance (see Image G-2 and G-3) of the genes showing. With 8 Agouti babies, the odds are pretty bad (actually 1 in 256) that Hank has any recessive genes. (Although, my own experience has seen this happen... 3 litters of all agouti and a blue self shows up in a litter!)  Then I get to thinking. Remember earlier when we said you can see only half of the rabbit. Look at image G-1 again. All the babies look just like Hank "A" but that is just the half we see. Every baby is also carrying a hidden recessive gene from Lucky "a".  Although they all look like Hank, they do not have the same "A-series genes". Every baby rabbit in the litter is carrying a dominant agouti and recessive self gene "Aa" (again see Image G-1). This gives me another choice. I could get rid of Hank (maybe sell him to someone that breeds agouti) and pick the best of Hanks babies to breed later on. After all I know that they all have Aa genes, and the next time I breed them to a self I'm going to get 50% selfs.

It's been 5 months since Hanks litter was born. I sold Hank to a young girl just getting started in 4-H. I sold 5 of the babies to the local pet store. I could tell they were not going to be the best of the litter. Now, I'm getting ready to take the remaining 3 rabbits (who happen to be all does) to a local rabbit show. I have some friends that will be at the show, and I want their advice on which rabbit is the best to keep. I also plan on trying to sell the remaining of the litter at the show.

6 months after Hanks litter was born and I'm down to one rabbit from the litter. I called the doe Maple and she reminds me alot of her father. There is another show in 6 1/2 months which makes this the perfect time to breed Maple. Hopefully I'll have some 5 1/2 month old self JR'S to show. This time, I breed Maple to Big Jimmy. Lets review.

We know Maple has Aa genes.  We know Big Jimmy has aa genes.

Now, let's look at Image G-4. Big Jimmys' aa genes are charted at the left
Maples' Aa genes are charted at the top. The red, green, yellow and blue
squares show the 4 possible outcomes. The red and yellow square babies have
the Aa make up. The green and blue square babies inherited the hidden self gene from
their mom. We now know the odds are 50% of the babies shoul be Agouti
with a hidden, self gene (Aa), and 50% of the babies should be Self (aa).






Part 3: I hate math

Lets take a moment to look at the odds of different size litters producing a self.
Don't let the math scare you. I'm putting a chart at the end for anyone not interested
in how to do the math.  (Of course, I know you are all now using the scroll feature on your mouse)

If Maple has a litter of one, there is a 1 in 2 chance or 50% chance there will be no selfs in the litter.
1/2^1=1/2 or 1/2*1=1/2

If Maple has a litter of two, there is a 1 in 4 chance or 25% chance there will be no selfs in the litter.
1/2^2=1/4 or 1/2*2=1/4

If Maple has a litter of three, there is a 1 in 8 chance or 12.5% chance there will be no selfs in the litter.
1/2^3=1/8 or 1/2*2*2=1/8

If Maple has a litter of four, there is a 1 in 16 chance or 6.25% chance there will be no selfs in the litter.
1/2^4=1/16 or 1/2*2*2*2=1/16

If Maple has a litter of five, there is a 1 in 32 chance or 3.13% chance there will be no selfs in the litter.
1/2^5=1/32 or 1/2*2*2*2*2=1/32

If Maple has a litter of six, there is a 1 in 64 chance or 1.56% chance there will be no selfs in the litter.
1/2^6=1/64 or 1/2*2*2*2*2*2=1/64

If Maple has a litter of seven, there is a 1 in 128 chance or .78% chance there will be no selfs in the litter.
1/2^7=1/128 or 1/2*2*2*2*2*2*2=1/128

If Maple has a litter of eight, there is a 1 in 256 chance or .39% chance there will be no selfs in the litter.
1/2^8=1/256 or 1/2*2*2*2*2*2*2*2=1/256

If Maple has a litter of nine, there is a 1 in 512 chance or .2% chance there will be no selfs in the litter.
1/2^9=1/512 or 1/2*2*2*2*2*2*2*2*2=1/512

If Maple has a litter of ten, there is a 1 in 1024 chance or .1% chance there will be no selfs in the litter.
1/2^10=1/1024 or 1/2*2*2*2*2*2*2*2*2*2=1/1024



















It is not uncommon for a rex rabbit to have a litter of five to eight. This provides a good chance that we will see most of the possible gene series combinations in any given litter. The offspring can tell us about their parents and vis versa. That's where record keeping comes in.
When we bought Hank, the owners kept no breeding records. This made it more difficult to determine what genes Hank had. I don't plan on making the same mistake. I started a pedigree for Maple and I'll do the same for her offspring. A pedigree is a chart that shows the rabbits family tree. I'll cover pedigrees in more detail later.

Part 4: What? Rabbits come in only two colors. You must be kidding.

Lets look at our second characteristic and put it to use.

The "B" series of genes determines if your rex rabbit will be Black or Brown (Chocolate).  There are only two genes in this series.

BBlack (dominate gene)     Causes the rabbits' coat to be black.

bBrown  (recessive gene)    Causes the rabbits' coat to be brown (chocolate). 

Let's take a look at these coat color genes, and a few examples of how to apply these genes to a breeding program.

I know, the first time someone told me there were only two colors of rabbits, I thought they were crazy, too.  But it's true. There are only two genes in the B series and they make your rabbits coat color either black or brown (chocolate). I know you have seen other colors, so have I. The other colors come from how different genes manipulate the actual pigments of the hair shaft.  There are black and yellow pigments in the hair shaft. They are an entirely different discussion and should not be confused with the B Series. There are also some modifers that make the yellow pigment orange to red. But we are jumping ahead of ourselves.  For now, lets just keep it simple. Black and brown (chocolate), that's it.

The A series gene gives us three different types of rabbit; agouti, otter, and self. The B series gene gives us two coat colors that we can apply to each of the three different types of rabbits. Lets take a look at the different combinations, and look at some photos. We can have black or brown(chocolate) self rabbits, black or brown(chocolate) otters, and black or brown(chocolate) agoutis.

In the examples below, I will mark the gene that is seen with its' corresponding letter, and the unseen gene with an underscore "_". There are six possable combinations.

1. A_B_        Black agouti (Called Caster on a rex)
2. At_B_       Black otter
3. a_B_        Black self 
4. A_b_        Chocolate agouti (Called Amber on a rex)
5. at_b_        Chocolate otter
6. a_b_         Chocolate self
 
1. Black agouti  (Caster)                               2. Black Otter                                            3. Black self











4. Chocalate agouti                                     5. Chocalate Otter                                      6. Chocolate self


              need photo                                                 needs photo









Part 5: The dilute gene, melanocyte cells, and melanin.

The "D" series genes determine how concentrated the color will be. 

D Dense (dominate gene)     Causes the melanocyte cells to produce a normal amount of melanin.

d Dilute  (recessive gene)    Causes the melanocyte cells to prdouce a reduced amount of melanin.

Skin, eyes, and hair all have a type of cell called melanocyte cells. These cells produce a pigment called melanin. The "D" series genes affect how much pigment (melanin) is produced by the melanocyte cells. Since these cells are present in the skin, eyes and hair, the color of all three will be affected by the "D" series gene.

The pigment (melanin) is also affected by uv-radiation (the sun). The sun causes the melanin to oxidize (to burn). This is what causes a suntan in humans. It causes the fur of a rex rabbit to fade and take on an 'orangish' cast. This is referred to as a 'sunburn' and is undesirable. It should be noted that this can happen very quickly.  Keep your show bunnies out of the sun. Hair cells are dead and cannot repair themselves. If your rabbit gets sunburned, you will have to wait for a new coat to come in.

I am not exactly sure if the "D" series gene simply decreases the amount of pigment produced, OR if it changes the black or yellow color in some way.  I have read, and been told, that the gene only reduces the amount of pigment being produced.  But, as we shall see in the next photos, it looks like more than that is going on.  I have, however, found sources that claim it works differently in different species. It can cause a reduction in pigment, a change in pigment, or both.  What is important, is how this gene looks on our bunnies. Lets take a look at how this gene works. 

In the examples below, I will mark the gene that is seen with it's corresponding letter, and the unseen gene with an underscore "_". There are 12 possible combinations.

1.  A_B_D_       Black agouti (Called Caster on a rex)
2.  At_B_ D_     Black otter
3.  a_B_D_       Black self 
4.  A_b_ D_      Chocolate agouti (Called Amber on a rex)
5.  at_b_D_      Chocolate otter
6.  a_b_D_       Chocolate self
7.  A_B_d_       Blue agouti (Called Opal on a rex)
8.  At_B_ d_     Blue otter
9.  a_B__d_      Blue self 
10. A_b_ d_      Lilac agouti (Called Lynx on a rex)
11. at_b_d_      Lilac otter
12. a_b_d_       Lilac self

Notice
When the black "B" gene meets the Dense "D" gene the color is black.
When the black "B" gene meets the Dilute "d" gene the color is blue.
When the Chocolate "b" gene meets the Dense "D" gene the color is Chocolate.
When the Chocolate "b" gene meets the Dilute "d" gene the color is Lilac.

Now, lets' look at some photos. I'll put the Dense "D" on the left and the Dilute "d" on the right.

       Dense "D" Gene                                                   Dilute "d" Gene

1. Black agouti (Caster)                                           7. Blue agouti (Opal)


                                                                             Need photo







2. Black otter                                                              8. Blue otter

                                                                                 Need photo








3. Black self                                                                9. Blue self

                                                                                 Need photo








4. Chocolate agouti (Amber)                                          10. Lilac agouti (Lynx)

Need photo                                                                    Need photo






5. Chocolate otter                                                         11. Lilac otter

Need photo                                                                   Need photo







6. Chocolate self                                                           12. Lilac self











Lets' take a look at how this gene effects eye color. The brown eye color of  the black and chocolate look, relatively, the same. The light blue-gray eye color of the blue and lilac look, relatively, the same. Notice the chocolate rabbit has chocolate eye color and when the dilute gene is added the fur turns to lilac and the eye turns to lilac.

   1. Chocolate eye color                                                                          2. Lilac eye color 

















    3. Black eye color                                                                               4. Blue eye color





















Genotype: All of the coded information (genes) from the mother and father to make all of the characteristics that make the entire rabbit.