Color Breeding in Pet Hedgehogs

Introduction:
      Health and temperament are far more important than color. Even when color breeding these should be the breeder's main concern: it does little good to get that long sought color if it manifests in a hedgehog with poor health that only unrolls to bite. Fortunately, as hedgehogs become more available, and most breeders are breeding for temperament it is not difficult to locate friendly and healthy hedgehogs in a plethora of colors.
      Building a herd of rare colors is very much a possibility, however, this can cost quite a bit of money considering that the rare colors tend to be priced higher. However, one does not necessarily need to buy a desired color in order to produce it. This page is designed to explain how to genotype a hedgehog and selectively breed for the colors that you wish to produce.

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Records and Techniques
      Record keeping is crucial to any breeding program, whether color breeding or not. Everyone's memory is fallible, and will not suffice as the only means of tracking crosses and results over time. In our era, computers add great convenience to being able to catalogue all of the matings you arrange in your breeding program and the outcomes of each. Keeping spreadsheets or databases with your records neatly tabulated provides excellent reference to contribute to building a great breeding program. Points of interest beyond color would be keeping track of individual health, size, and temperament. There are also several pedigree programs available to electronically record the lineage of your breeding stock.
      Still, it is beneficial to keep paper record as well. A calendar specifically for your hedgehogs is a great start. Mark everything on the calendar and when the year is over you can file the calendar and use it as future reference. It is also a good idea to keep a pedigree of each hedgehog on the front of their cage. For the improvement of a color breeding program the pedigrees should include the color of each individual in the breeder's lineage and the genotypes (genetic makeup), wherever it is known. This will give you an immediate idea of which crosses could yield which colorations, as well as keeping you aware of any recessive traits, such as snowflake or albinism, that have skipped several generations.
      Once you have a sound record keeping strategy, you will start to develop a better sense of which crosses will yield the best results, and the desired colors. At this point you could be tempted to cross related individuals in order to bring out a rare color. However, this is a risky practice to undertake: heterozygosity, in general, improves the health of an animal, and inbreeding or line-breeding reduce this (i.e. genetic diversity in a breeding program is diminished through breeding related animals). In theory, line-breeding will improve your animals over a relatively short number of generations; however, this only works if your judgment is sound and educated on choosing which individuals to keep back as breeding stock (and it is not as easy as it might seem).
      For the sake of preserving what genetic diversity is available in the pet hedgehog (and, due to importation bans, this is already low) it is strongly recommended that one does not line-breed any closer than five generations back; that is to say, only crossing individuals that share common ancestors that are five generations back in their pedigrees or further.

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Determining Genotypes
     There are usually three aspects considered when genotyping an animal-- the animal's color, its parents' colors, and the color of its offspring. Unless a hedgehog is an albino you should be able to fill in about half of the genotype just by looking at it.
     From here a test cross can be made in order to determine which alleles are being carried: a test cross is the method of crossing an animal with a known genotype to an animal with an unknown genotype in order to fill in the unknown's genotype or test the accuracy of the known's. For an example, say that you have two dark colored hedgehogs- one was born from a chestnut x apricot cross, giving it the genotype B/b;Ru/ru, while the other's parents are unknown so we can only assume that it has at least one B allele from how dark it is, written as B/-;-/- (the hyphens act as place holders for unknown alleles). When the cross of these two individuals yields two chestnuts, a cinnamon, and an apricot we can now safely assume that the second hedgehog's genotype is the same as the first's, which is B/b;Ru/ru. We know this because this is the genotype that can produce all of these colors when paired with the known genotype. The genotype of an apricot is b/b;Ru/Ru, while the genotype of a cinnamon is b/b;ru/ru, the only way both of these can result from the same cross is if both parents have at least one b allele and the genotype Ru/ru at the ruby-eyed dilution locus.

Test Cross Walk-Through
Our Hedgehog = Black based color that appears tawny
His Mother = Tawny
His Father = Cinnicot

     We will start by trying to fill in as much of his genotype as possible by looking at him. Our first observation should be that he is not an albino, so we know that he has at least one C allele: however, we do not know if he is carrying albinism, so for now we will put a dash in the second space of the C locus to show that it is unknown, as such C/- . The next thing we want to know is his base color - although he looks very brown-toned we must remember that the agouti trait adds in red-orange pigments, you should take note of how dark his skin is, and the fact that the centers of his color bands are also very dark; he is a light shade of a black based color, which means that he has a B allele. This time we can fill in both spaces of the locus because we know that his father was a cinnicot (which is a brown based color) so he also has a b allele (C/-;B/b). Now we will check for modifiers. Although he looks very tawny colored, we cannot safely assume that he has a ruby-eyed allele just by looking at him (agouti expression has the potential to mimic ruby-eyed dilution in the coat), and neither of his parents are apricots or argentes; however, he is not argente colored, so we can assume that he has at least one ru allele (C/-;B/b;ru/-). He does not appear to have any blue-fawn dilution so he has at least one D allele, and neither of his parents were dilutes so we do not know if he is carrying a d allele; as before we will have to put a dash in the unknown space of this locus (C/-;B/b;ru/-;D/-). He is not a snowflake and is likely old enough that he will not flake-in, so he has at least one Sn allele, we do not know if he is carrying an sn allele because neither of his parents are snowflakes.

We have already determined that his genotype is C/- ; B/b ; ru/- ; D/- ; Sn/-.

     To determine the remainder of his genotype we will cross him with females with known genotypes.

A Test Cross:

     We now know that he has one c allele since there were two albinos (cc) produced, and one Ru allele because there was an apricot. His known genotype has expanded to C/c;B/b;Ru/ru;D/-;Sn/-

Another Test Cross:

      The amber was a dilute color, so we now know that he is carrying the allele for dilution. There was also a snowflake color produced so he is also carrying sn, the snowflake allele.
      His genotype is now known to be C/c;B/b;Ru/ru;D/d;Sn/sn. We were able to determine his genotype just by looking at him and using two test crosses. Once you have most of your hedgehogs genotyped you will have a better understanding of which genes their offspring are carrying and will be able to make informed decisions on what crosses to make in order to get desired colors.
      Now you may be wondering how you are supposed to be able to fill in an unknown genotype if you do not have any hedgehogs with known genotypes to use in test crosses. The method that must be used in these situations is to make a test cross per unknown locus. For instance, if you have a hedgehog with a known genotype at only one locus you can use it for test crosses to determine the genotype of that locus on another hedgehog. This does make for a relatively slow process, but after a few generations you will have a great knowledge of the genes that are in your herd's gene-pool.

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Making Strategic Crosses
      Once you have an understanding of the genetics described on the previous pages and you are able to decipher the genotype from phenotype then you can begin to breed for those colors that you would like.

Rainbow Litters
      The easiest way to produce litters of various colors (so called rainbow litters), is to cross a tawny colored hedgehog who had a brown base-colored parent (cinnamon, cinnicot, or apricot) to a hedgehog that is a brown base-color (cinnamon, cinnicot, or apricot); the more recessive traits shared by the two parents in their pedigrees the better (blue-fawn dilutes, snowflakes, and albinos).
      The only real trick here is heterozygosity; the more heterozygous loci between a cross, the more diversity will be seen in the offspring. Like in the first example given in the genotyping section: two dark colored hedgehogs were able to produce such a wide variety of the principle colors because both were heterozygous at the B and Ru loci (i.e. they were both tawny colored).

Statistics
      Genes are as simple as mathematic factors. You can determine the probability that each offspring has of being a particular color if you know the genotypes of the parents. By using FOIL (a mathematic factoring technique: First, Outside, Inside, Last) or a Factor Table (Punnett Square) for each trait you can accurately predict which colors might result from a particular cross.

Argente x Cinnicot [both with known genotypes]
(C/c;B/b;Ru/Ru;D/D;Sn/sn) x (C/c;b/b;Ru/ru;D/d;Sn/sn)

      The D locus shall not be considered in this example since the sepia parent is homozygous D, no dilutes are possible from this particular cross, although each offspring has a fifty percent chance of being a carrier. This still leaves four loci that need to be considered in order to predict the colors of this cross. Since a Punnett square for four traits would require 256 blocks, it is better to use a branched line method to determine the phenotypes, as is shown below. Before we can set this up we have to know the probability of the cross of each loci that is being evaluated. I have provided these here; you can get them by setting up a Punnett square for each trait. With experience you will eventually learn which crosses yield which probabilities without any need to set up squares or use any other method.
C/c x C/c = 3/4 C- , 1/4 cc
B/b x b/b = 2/4 Bb , 2/4 bb
Ru/Ru x Ru/ru = 2/4 RuRu , 2/4 Ruru
Sn/sn x Sn/sn = 3/4 Sn- , 1/4 snsn

Resulting in...

     These percentages will not be seen in each litter. The Punnett square only shows which colors are possible and of those colors which are most likely to occur. For example, making this cross only once might result in two albinos, one argente, and an apricot. To read more about the application of Punnett squares read the Introduction to Color Genetics page.

The Cross Table
      I have constructed a table of all of the possible principle color crosses (not including their blue-fawn dilute variants), showing the probability of offspring phenotypes. I present it here as a tool for other color breeders of hedgehogs to utilize.