Return
Basics of Color Breeding
By Jill Pfaff & J. Ross

This article is intended to explain the basics of Color Breeding in rabbits. How to improve the type of a color variety by using other color varieties. And why certain colors are limited to being bred to only certain other colors. This article also explains how to use a punnet square for predicting possible trait outcomes of litters.

A lot of old timers will give you the advice that you should only breed together the same color of rabbits with a few exceptions. This is sound advice! As discussed in Genetics 101, rabbits carry two copies of every gene. A rabbit that is homozygous (having the same alleles for a gene) will show better coat color than a rabbit that is heterozygous (Having different alleles for the same gene.) There are some exceptions to this basic rule, as there always are, there are colors that depend upon the rabbit having a homozygous combination of alleles for the proper color. This is mostly found in the rabbits of the various chinchilla varieties.

What's a punnet square?

A punnet square is used to predict the genotypes of offspring from a cross between two rabbits. It also predicts the ratio of those genotypes. Figure 1.0 shows a typical setup for a punnet square. Don't worry if it looks confusing. We'll be going over several examples, you can also e-mail J. Ross or Jill with questions.

Figure 1:Typical Punnet Square
Buck's Name, 
Trait, 
(Genotype for Trait)
Sperm Type 
"A" from 
buck
Sperm Type 
"B" from 
buck
Egg Type 
"A" from 
doe
Kit "A"
Kit "B"
Egg Type 
"B" from 
doe
Kit "C"
Kit "D"
Dam's Name,
Trait,
(Genotype for Trait)

We suggest that you read over the Genetics 101 article also on this web site first to help with terminology and concepts we will be using.

How is a punnet square useful to me?

As stated before a punnet square is useful in predicting what color of kits to expect from a mating. It also allows you to figure out if either parent is carrying any recessive genes. This is done by comparing what you expect the outcome to be and what the outcome of the mating actually is. When used in combination with pedigree analysis you can predict the colors in your litter with a high degree of accuracy. You must keep in mind when using a punnet square that just because the color is possible in the cross it will not always show up. When using a punnet square you are dealing with chance. A roll of the dice or a flip of the coin. If the same two rabbits are mating together enough you will eventually see all the colors predicted by your punnet square IF the genotypes you assigned to the rabbits are correct.

How do I use a punnet square?

Figure 1. shows a standard punnet square and how it is filled in. Let's try one together. First Lets Draw our square. Figure 2 shows a totally blank punnet square. the "X" in the upper left hand corner indicates this is a cross. Similar to when you write our Buck X Doe. Notice the double lines. They help separate the predicted sperm and eggs cells from the kits. This only helps in the clarity of the table, making it easier to understand. Also notice that the buck's name, trait of interest, and genotype of trait of interest is written along the top of the table. The doe's name, trait of interest, and genotype of trait of interest is written along the left hand side. This is a standard layout.

Figure 2:Blank Punnet Square
Buck's Name, 
Trait, 
(Genotype for Trait)
Dam's Name,
Trait,
(Genotype for Trait)

Let's start with our first example of how to use a punnet square by mating a pair of New Zealand Whites that produce offspring with buck teeth ( Click here to print of the next set of problems to follow along!). The allele symbols we will use for buck teeth will be N for the normal tooth allele and n for the buck tooth allele. This means the following:

NN rabbits will have normal teeth and will NOT be a carrier of the buck tooth allele
Nn rabbits will have normal teeth and WILL be a carrier of the buck tooth allele
nn rabbits will have buck teeth and will only be able to pass on the buck tooth allele.
In example we have two rabbits with normal teeth but, when they are mated together they produce offspring that have buck teeth (Remember that for an offspring to show a recessive trait, BOTH parents must carry the allele). What genotype would you put down for them? See figure 3 for the correct genotype for both rabbits.

Figure 3 also shows our next step. Since each rabbit comes from the union of one egg cell from the doe and one sperm cell from the buck, we must predict what alleles each egg and sperm will carry. And then we must predict what traits each kit will inherit.

Figure 3:Punnet Square Problem 1
YD's Sneaky Pete, 
Normal teeth: 
Buck tooth carrier, 
(Nn)
YD's Sassy Sally,
Normal Teeth: 
Buck tooth carrier,
(Nn)

Egg and sperm cells only carry one allele for each gene. If they carried two copies, the offspring would have four copies of each gene, and then their offspring would have eight copies of each gene. The basic way this is accomplished is through meiosis. We will simplify meiosis to the following concept: The process by which one cell divides into two cells; dividing it's genetic material equally between each of the two "new" cells.

In our punnet square we must decide which allele each sperm cell carries. The buck has one N and one n. This means a sperm cell can only carry a N or a n for the buck tooth trait. So now we assign each of the two sperm cells an allele. We assign one sperm cell the N allele and one sperm cell the n allele. It is common practice to list the most dominant allele on the left and the most recessive allele on the right (You will see why at the end of this example). Next we must decide which allele each egg cell carries. The doe also carries one N and one n. So we assign one egg cell the N allele and one egg cell the n allele. On this side of the punnet square we place the most dominant allele on top and the most recessive on the bottom. We have now completed assigning alleles to the egg and sperm cells. Next we will combine the egg and sperm cells into rabbits!

Figure 4:Punnet Square Problem 1
YD's Sneaky Pete, 
Normal teeth: 
Buck tooth carrier, 
(Nn)

YD's Sassy Sally,
Normal Teeth: 
Buck tooth carrier,
(Nn)

We will now create our offspring to see what traits they will have. We do this by coping each of the sperm cell's alleles down each column and each of the egg cell's alleles across each row (Notice the direction arrows in figure 5). The punnet square looks a bit cluttered. Take a minute to study it and see how the graphical representations match the text.

Figure 5:Punnet Square Problem 1
YD's Sneaky Pete, 
Normal teeth: 
Buck tooth carrier, 
(Nn)


N + N = NN+ =
N + n = Nn+ =
n + N = Nn+ =
n + n = nn + =
YD's Sassy Sally,
Normal Teeth: 
Buck tooth carrier,
(Nn)

Now we have a litter of four kits (Figure 5). We must determine how many kits are a) normal (NN), b) normal and carriers (Nn), c) buck toothed (nn). Fill out these questions on your sheet that you printed off earlier. Count the number of kits with each genotype and make a fraction for each one by putting the total number of kits for each genotype over four (The total number of kits in the litter).

You should get the following results. a) 1/4, b) 2/4, c) 1/4. While this cross doesn't produce a large number of buck toothed rabbits, it does produce a large number of buck tooth carriers. This is the main reason to cull known carriers of negative reccesive genes out of a breeding program. You will generate 2 carriers of the bad trait to each non-carrier rabbit produced. If you do find that a peticular cross generates rabbits that display defective traits, such as buck teeth, you should notify all the other breeders you have sold stock to. You should also test cross all the offspring you have back to the parents (known carriers) to see which offspring are also carriers .

Figure 6 shows a punnet square filled out without the graphical representation. This is what a typical punnet square looks like on paper. Figure 7 below shows the steps in using a punnet square on paper. Try problem #1 again on your own. Then try problem #2. Scroll down to see how to work problem 2.

Figure 5:Punnet Square Problem 1
YD's Sneaky Pete, 
Normal teeth: 
Buck tooth carrier, 
(Nn)
YD's Sassy Sally,
Normal Teeth: 
Buck tooth carrier,
(Nn)

Figure 6:Punnet Square Problem 1
YD's Sneaky Pete, 
Normal teeth: 
Buck tooth carrier, 
(Nn)
N
n
N
NN
Nn
n
Nn
nn
YD's Sassy Sally,
Normal Teeth: 
Buck tooth carrier,
(Nn)

Figure 7: Problem Summary

How can I improve my line by using other color varieties? (Problem #2)

Return