Overview of Hedgehog Colors: Part 3 of the Color Breeding Series

Hedgehogs are relatively new arrivals to the pet hobbyist scene, and the views on their colors have changed considerably over the years. It has been theorized that initially, there were two main species of African hedgehogs imported to the U.S. as pets, the White-Bellied hedgehog and the Algerian hedgehog (it should be noted that some have noted that the two species that were crossed to create the pet hedgehog may have actually been two regionally separated groups of white-bellied hedgehogs, with no Algerian ever being crossed in). The colors of the two different varieties of hedgehog were similar, but were believed to be distinguishable and show variance in heritability. They both had a black coloration and a brown coloration, although the black colors were not considered to be different by many breeders (creating three colors: Standard, Brown, and Algerian Brown). Crossing the two different brown colors yielded the first known orange colored hedgehogs. Since the initial identification and naming of the colors, a plethora of other shades have been described and named, producing color standards for ninety-two colors currently recognized by the International Hedgehog Association. The interesting quality behind this brief history is that the earlier concepts of hedgehog colors appear to have been closer to the truth than the over-complicated naming system that is currently in common use. The current system names every possible shade along a gamut of colors, without any regard to how they are inherited.

From a study on the inheritance of color in hedgehogs, it has been determined that there are two base colors present in pet hedgehogs, black and brown (or gray and cinnamon, respectively). A second genetic locus (that of the ruby-eyed dilution gene) modifies the appearance of these two colors to produce the other principle colors seen in hedgehogs. If it is assumed that the history behind the colors is correct, then it would have been a Cinnamon x Chocolate/Brown cross (both of which are different shades of brown in appearance) that yielded the first Cinnicots and Apricots (or {bbruru} x {BbRu-} = {bbRuru}, etc.). For a quick tutorial on coat color genetics read: Introduction to Color Genetics.

The semi-expressive qualities of the ruby-eyed dilution trait account for much of the color variations possible in hedgehogs. It dilutes both the black based colors and the brown based colors to an orange-overcast-brown and orange, respectively, but can show either complete, incomplete, or co-dominant expression in the coat. Therefore, under its affect Gray becomes either Chocolate or Brown, and Cinnamon either Cinnicot or Apricot; creating six principle colors in hedgehogs, or twelve when considering the blue-cream diluted variants of these six principle colors.

There are dilute versions of the black-based colors and the brown-based colors. However, there seems to be complications involved in producing diluted black-based colors (Opal, Blue-Fawn, and Fawn), with these three colors being far more difficult to produce than the diluted brown-based colors (Silver-Cinnamon, Silver-Cream, and Cream). Whether or not this is due to problems with incompatibilities between the black and dilute genes or just from gene distribution in the whole pet hedgehog population is still unknown.

Beyond the principle colors there are also a few modifiers present in pet hedgehogs. These traits include snowflake, pinto spotting, and albinism. Both albinism and snowflaking are the result of simple recessive genes (denoted as cc and snsn, respectively), although there could also be another trait that mimics snowflake with a dominant mode of inheritance (Roan: Rn-). Pinto spotting is a dominant trait (S-), but is variably expressive and appears to be capable of skipping generations from time to time (“hidden pintos” might have a pinto freckle here or there).

When considering the six principle colors, along with their blue-cream dilutes and the possible combinations of the common modifiers there is a potential for forty-nine distinct coloration in pet hedgehogs.

Black Based ColorsBrown Based Colors
GrayCinnamon
ChocolateCinnicot
BrownApricot
BlueSilver-Cinnamon
Blue-FawnSilver-Cream
FawnCream
Modifiers
Albino
Snowflake
Pinto

The Agouti Pattern

The most important thing to remember, when considering the expression of hedgehog colors, is that hedgehogs are agouti (pronounced: uh-goo-tee) patterned animals. There are not any self-colored hedgehogs in the ‘domestic’ bloodlines, at least not yet. Being agouti patterned means that there is an extra pigment in the hair/spine coloration (this extra pigment is the tan/orange melanin known as pheomelanin— the common black/brown pigment is called eumelanin).

Hedgehog Spine

This means that a black hedgehog will never be just black, but, instead, will always have black and tan on its spines. However, the very rare color known as Salt & Pepper is supposedly an exception to this; if they truly are lacking the agouti-induced tan bands, then they could be a different type of color: not necessarily self-colored, but some form of color inhibition– comparable to a silver tabby cat. For the time being, the Salt & Pepper coloration will be set aside. Note in the image above that the base-color appears in between the two agouti-induced bands. The base-color band is indicative of the color genes present in the hedgehog, i.e. whether it is a black or brown based color. However, the shade of the base-color band can also be diluted by overlapping of the agouti bands, which can make black bands look like more of a deep chocolate-brown color.

The main issue that arises with agouti patterns is how much of a color range can exist. A black agouti can have an overall appearance of almost black, uniformly black and brown, or, seemingly, entirely brown. It can be pretty confusing for some people when you hold up a black hedgehog next to a brown one and say “these are the same color”. However, this is not a unique phenomenon; for instance, some brown tabby cats look mostly black next to others that look almost chocolate— brown tabby can be considered an homologous color to black agouti hedgehogs: i.e. the same color within different animals. Breeders of other small animals have reduced this problem by either setting up strict guidelines for what shade an agouti color should be, or by classifying all black agoutis and brown agoutis into one category (the latter, for obvious reasons, would not be a very helpful standard for animals in which agouti is the only pattern).

The overall appearance of the hedgehog depends on the ratio of tan-to-black coloration, not just in the bands, but also in the skin. The agouti-induced pigments accumulate in the skin as they do in the hairs and spines, which can be observed by noticing that the skin color is proportional to the amount of tan on the bands without the presence of modifiers. For instance, if a chestnut colored hedgehog had as much tan on its bands as is shown in the image of the spine above, then its skin would not be truly black, but would instead be very dark brown (still appearing black to some).

The ranges produced by this phenomenon can create an overlap in the outer ranges of various phenotypes, often making it difficult to determine the color of any hedgehogs that are outliers; for instance, a gray hedgehog with considerably more agouti expression than the average amount can be as light as a hedgehog that is genetically chocolate. Likewise, a very dark Chocolate can be darker than some Grays.


Age Related Fading

Age related fading is one of the greatest complications in identifying hedgehog colors. While it is more noticeable in the darker colors it can affect them all. However, it doesn’t affect all hedgehogs, and not all of the hedgehogs that are affected fade out to the same degree, which could indicate a heritable factor.

Ericius 1 yr
Ericius 3 yr

 The trait expresses as an overall reduction of the color intensity as the individual ages, black fading to brown (as is illustrated on the left). Such an occurrence can create issues when it comes to identifying a hedgehog’s color. However, it takes a few years for the color to fade as drastically as is shown here: the Gray hedgehog pictured above is three years old in the photo on the right, which is beyond the age of most hedgehogs’ reproductive age. This reduces the odds of misinterpreting a phenotype due to age related fading when color breeding. The fading usually begins around eight to thirteen months of age, with a slow progression. In some individuals the fading eventually stops, while in others it continues throughout their life.


Juvenile Colors

Slithy Tove 16 Days

The process of pigmentation begins shortly after birth; all baby hedgehogs are born colorless with closed eyes. Pigmentation is typically noticeable in the skin by day two for darker colored hedgehogs, and a few days later for lighter colors, depending on how light; creams might even appear to be albinos until their adult spines grow in. The initial coat colors that appear are often in shades of gray or off-brown. After the first couple weeks of age a second baby coat will begin to grow in: this second coat will usually reveal more of the color that the baby will grow to be, although many of the spines are likely to still be banded by the various shades of the baby grays (the Gray colored baby on the left is sixteen days old, notice how she already has many Gray colored spines along with some that still banded by dark silver).

The eyes tend to open between 15 and 20 days of age, or around two weeks old. The eyes of Grays will be black, while the eyes of Cinnamon babies can appear anywhere from light brown to nearly black when they open. The eyes of a Chocolate or Brown babies are most often black in appearance when they open but occasionally will be dark ruby-red and then darken to black, or near black, with age. The eyes of Cinnicots are most often ruby-red when they open and may or may not darken with age. Apricots eyes are ruby-red when they open and then remain so.

The final quilling process can take place any time between four and twelve weeks of age. After this process is completed a hedgehog has attained its adult coloration. The only changes that are still likely to occur would be snowflaking or roaning, which can happen fairly late in some cases. If the hedgehog is pinto or albino it will be notable from the onset of pigmentation (or, rather, the lack thereof).


Ryan is a guest writer. He has years of experience with coat color genetics, experience with hedgehogs since 1995, and began studying their color genetics in 2001.He earned his degree from Oklahoma State University, College of Arts and Sciences, Department of Microbiology and Molecular Genetics.

Introduction to Color Genetics

This post was designed to be a quick guide to help explain some of the basics of coat color genetics: including basic concepts, and vocabulary. Many animal breeders shy away from genetics, thinking it is either not necessary or that genetics are too complicated to be worth while. I believe that it is important to understand the genetics of the animals you breed. Even if it is something as seemingly trivial as color genetics, it will pave the way to helping you understand the inheritance of other traits so that you can do your part for improving the health, appearance, and overall quality of the species.


What are Genes?

A gene is a small piece of a big molecule called DNA, and exist inside living cells in a ‘wound-up’ DNA molecule known as a chromatid— two identical sister chromatids are joined together to form the structure known as a chromosome.

DNA is a molecule, but is also a type of code that can be compared to an instruction manual. Mechanisms inside a cell read the DNA, which instructs the cell to make a product or perform a task.

In color genetics, symbols (usually a letter) are used to refer to a gene’s location within the DNA molecule. These locations are called loci (singular: locus). For example, the ‘A locus’ of mammal colors is the location of the Agouti gene (agouti is a trait that causes bands of different colors to occur in each hair).

One gene can have multiple variations, and these variations can result in very different outcomes for the animal. These variant forms of a gene are called alleles. The alleles of the Agouti gene that we will discussed here are A (agouti), and a (not agouti).

An individual inherits its genes directly from both of its parents, because of this everyone will have two alleles for each locus. The combination of these two alleles is known as the genotype. If an individual inherits an A allele from its mother and an a allele from its father then its genotype for the A locus is Aa.


Basic Terminology

Dominant and Recessive

When there are two different alleles at a locus, such as with the genotype Aa, it is often the case that only one of the alleles will show a noticeable result in the individual’s physical appearance. This is because of the phenomenon known as dominant and recessive expression. If an allele expresses when there is only one copy of it in the genotype then it is classed as a dominant gene. While an allele that only expresses when it has two copies in the genotype is classed as a recessive gene.

Dominant alleles are traditionally written in caps, while recessive alleles are lower case. If there are more than two alleles present at a locus, then superscript is used to distinguish between the multiple alleles and the hierarchy becomes less obvious (E.g. Aw,Ay,a).

For the Agouti locus the A allele is dominant, while the a allele is recessive. So an individual with the genotype AA or Aa will be agouti colored, while an individual with the genotype aa will be non agouti, i.e. solid colored.

Phenotype and Genotype

The genetic term for the physical appearance of an individual (such as color) is ‘phenotype‘. An individual with the genotype Aa is said to have an Agouti phenotype, while an individual with the genotype aa is said to have a non-agouti phenotype.
Genotype = The actual genetics of an individual.
Phenotype = The visible expression of an individual’s genotype.

Homozygous and Heterozyous

These are the terms used to describe whether or not a genotype is composed of like alleles. If a genotype is composed of like alleles (such as AA or aa), then it is said to be a homozygous genotype. If a genotype is composed of two different alleles (such as Aa), then it is said to be a heterozygous genotype. It is quite common in the world of color breeding to hear people use the abbreviation ‘het’ when referring to an animal with a heterozygous genotype for a desired recessive trait.

Terminology Summarized

Allele-MatchGenotypePhenotype
HomozygousAAAgouti
HeterozygousAaAgouti
HomozygousaaNot Agouti

Inheritance

Inheritance can get complicated, but coat color inheritance is often a very simple mechanism: when two individuals are crossed, half of each of their genotypes goes to their offspring. This means that if an individual has the genotype Aa, then it will pass either an A or an a to each offspring; while the offspring would get the second half of its genotype from the other parent. Where the process can get complicated is when considering more than one locus.

The B locus is the location of the Black/Brown gene, of which two alleles will be discussed for this tutorial: the dominant B allele (black) and the recessive b allele (reduced to brown). The agouti locus is epistatic to the B locus, which means it changes the normal expressions of the B locus, or in other words, the expression of the B locus is reliant on the affects of the A locus.

The genotype {AA BB} will produce a black agouti, sometimes called golden agouti or brown (hairs are banded by black and tan/orange, like a brown tabby cat), while the genotype {AA bb} will produce a brown agouti, very commonly known as a cinnamon (hairs are banded by brown and tan/orange). However, without the dominant agouti gene the banding affect goes away; the genotype {aa BB} will produce a solid black colored individual, while the genotype {aa bb} will produce a solid brown colored individual.

Many more traits can be taken into consideration to get an even larger and more complex genotype. The main color loci in most mammals are  A (agouti),  B (brown),  C (albinism),  D (dilution), and E (color extension).

Punnett Squares

The chance that an offspring has of inheriting certain allele combinations from its parents are frequently determined using a tool called a Punnett Square. This simple tool shows which allele combinations are possible in a particular cross.

For an example, say two individuals are crossed, and one is black with the genotype BB, and the other is brown with the genotype bb. The Punnett square would be set up as is shown below– with the genotype of one parent written along the top, and the genotype of the other written along one side.

Punnett Square Unfilled

Then in each box within the square combine the allele above it with the one to its left. The results can be seen in the square below. Each box represents the genotype of a potential offspring.

Punnett Square

There is a 100% chance of getting black offspring. Each of the parents had only one allele of the B locus to give, the one whose genotype is written across the top of the square could only give a B allele, while the other parent, whose genotype is written on the left side of the square could only give a b allele.

If you were to cross two individuals who both had the genotype Bb, then the results would be as follows.

Punnett Square

Each baby born from this cross would have a 50% chance of being heterozygous black, a 25% chance of being homozygous black, and a 25% chance of being brown (overall, an offspring of this cross would have a 75% chance of being black colored, and a 25% chance of being brown colored; i.e. the cross yields a 1/4 chance of producing brown).

Now let’s will look at multiple genes. If you are wanting to track traits from more than one gene, then you can either set up multiple Punnett squares and divide the percentages down to the final statistics, or you can combine the genotypes into a single large square, see below.

For this example lets go back to our Agouti and Black genes. If we were to cross two individuals with genotypes {Aa Bb} and {Aa bb} (a het black agouti, and a brown agouti), then we would begin by factoring the genotypes of each parent, and then apply those to the square. Parent number one with the genotype {Aa Bb} can give the following combinations to its offspring: A B, A b, a B, and a b. Parent 2 with the genotype {Aa bb} can give: A b, A b, a b, and a b. We will put parent one along the top of the square, and parent two on the side.

Punnett Square Multiple Genes
Black Agouti6/1637.5%
Brown Agouti6/1637.5%
Solid Black2/1612.5%
Solid Brown2/1612.5%

Due to the fact that the genes are combined randomly, the percentages that a Punnett square calculates do not apply to each litter. In other words, one litter from the cross above could consist of all solid colored offspring, but if the cross is repeated many times, then the percentages from all of the crosses will begin to converge on those of the Punnett square. Punnett square determines the percentages produced from crosses within a population, or the probability per individual.
     Simply put, the Punnett square is just a tool: it is very useful to see which colors are possible in a cross, and which of those is more likely to occur. It does not make predictions.


Linked Genes

So far we have seen that multiple traits are assorted independently; where {Aa Bb} crossed with {Aa bb} yields the product of two independent ratios 1AA:2Aa:1aa x 1Bb:1bb. However, if the A-locus and the B-locus were close to each other on the same chromosome, then the allele combinations between the two loci would remain the same from one generation to the next. They would not be independently sorted and would then be called linked genes (this is just for an example, the black and agouti traits are not linked in any animals that I am aware of)

The genotype of linked traits is written differently; since the two alleles of different loci are linked together they must be written in a way that shows this linkage. For example, if one individual had inherited an A allele and a B allele next to each other on the same chromosome from one parent, and from the other parent they inherited a chromosome with an a allele next to a b allele then that individual’s genotype for these two loci would be written as {AB/ab}. This shows that on one chromosome the dominant allele of the A-locus is linked to the dominant allele of the B-locus, while on the other chromosome the recessive alleles of the two loci are linked. 
      If A and B were linked and the above cross were made, then the outcome would be very different. I will now set up the same cross again, this time showing that the two loci are linked.

Punnett Square Linked Genes
Black Agouti2/450%
Brown Agouti1/425%
Solid Brown1/425%

As you can see, the result is greatly different when the traits are linked together. Since the only B allele is linked to an A allele, it is impossible to get a solid black from this cross. But fortunately, the black and agouti traits are not actually linked.

Unfortunately, if you are tracking linked traits, then there is no shortcut method of figuring out the allele combinations, you will have to keep detailed color-pedigrees and track the genotypes of each generation.


Hedgehog Colors: For Color Breeding

Ryan is a guest writer. He has years of experience with coat color genetics, experience with hedgehogs since 1995, and began studying their color genetics in 2001. He earned his degree from Oklahoma State University, College of Arts and Sciences, Department of Microbiology and Molecular Genetics.

A Little Info Before We Begin

It is important to understand that these are not the show standard hedgehog colors as accepted by the International Hedgehog Association, the color groups in this post have been developed for accurate predictive color breeding. For the show standards of hedgehog colors please visit the IHA Color Site. To read the study with supporting data for the genotypes and color groups used here, then check out this article: Inheritance of Coat Color in African Pygmy Hedgehogs.

Hedgie Color Genetics

From the perspective of color breeding, there are four fundamental colors of hedgehogs. Gray, Cinnamon, Chocolate, and Cinnicot. Brown and Apricot are genetically the same as Chocolate and Cinnicot, respectively, but are extremes of a variable color expression. For example, a hedgehog with the genotype {Bb Ruru} will have a much higher probability of being born Chocolate than Brown or Gray, but the dominant Ru gene is quite variably expressive and can result in any color between the two extremes of Gray and Brown. The same is true for {bb Ruru} hedgehogs, which will most likely present as Cinnicot, but could range anywhere from Cinnamon to Apricot.

This unfortunate reality can make it difficult to breed exclusively for Browns or Apricots, but developing pure lines of {BB RuRu} (Chocolate/Brown) or {bb RuRu}(Cinnicot/Apricot) will significantly increase your odds. From there, one would selectivity choose breeders who fully express the Ru traits.

Beyond the fundamental colors, there are blue-cream dilutions, which are particularly easy to identify in the Cinnamon to Apricot range, but appears to have complications in the Grays (blues). This brings the potential number of base colors to eight: Gray, Blue, Cinnamon, Silver-Cinnamon, Chocolate, Blue-Fawn, Cinnicot, Silver-Cream. With Fawn and Cream being genetically identical to Blue-Fawn and Silver-Cream, respectively (dilute forms of Brown and Apricot).

One final note, pet African hedgehogs are agouti colored animals, light-bellied or white-bellied agouti to be specific (hybrids of both). All this means is that the type of melanin (color pigments) in the hair (or spine) changes from the black/brown eumelanin to the orange/yellow pheomelanin along the length of each hair (or spine). Note that on hedgehogs, the colors in the spines shift from beige/white, to tan/orange/yellow, to the base color, then to tan/orange/yellow again before returning to beige/white. This shift is known as an agouti pattern and is clearly present in hedgehogs. The white break on either side of the bands is not necessarily part of the agouti pattern, but is not uncommon- see tabby cats.

The agouti pattern becomes significant because, just like the Ru trait, it is also variably expressive: the more pheomelanin produced, the lighter the hedgehog will appear. For example, a Gray hedgehog can have very little pheomelanin production resulting in more black on the spines and darker skin, or a lot of pheomelanin production and look very muddy colored with lighter skin. Once again, to see a more familiar example of this, look at the variability of brown tabby cats: essentially, all hedgehogs can be considered to be tabby colored, and if this is more familiar and easier to approach than calling them ‘agouti’, then go for it.

B/- ; ru/ru ; D/-Gray
b/b ; ru/ru ; D/-Cinnamon
B/- ; Ru/- ; D/-Chocolate
b/b ; Ru/- ; D/-Cinnicot
B/- ; ru/ru ; d/dBlue
b/b ; ru/ru ; d/dSilver Cinnamon
B/- ; Ru/- ; d/dBlue Fawn
b/b ; Ru/- ; d/dSilver Cream
Hedgehog Pigmentation Pathways

The Base Colors


Albino {cc — — –}: While not technically a base color, albinism masks any colors that a hedgehog might genetically be. There is no pigmentation present in the skin, which is pink in appearance.  No Pigmentation in the eyes, which appear red.  And no pigmentation in the spines, which will be solid white. If there is any pigmentation present, then the hedgehog is not an albino.

Photo by Ryan DickeyPhoto by Ryan DickeyPhoto by Ryan Dickey

Gray {C- B- ruru D-}: The pigmentation of the skin ranges from black to brown in appearance with black eyes and a dark mask on the face. The coat coloration is typically black with tan-orange banding on either side of the principle coloration.

Photo by Ryan DickeyPhoto by Ryan DickeyPhoto by Ryan Dickey

Chocolate {C- B- Ru- D-}: Exhibit characteristics of either Gray or Brown with co-expression in the coat coloration: containing a mixture and blending of some black banded spines and some brown banded spines, with amounts varying per individual.

Photo by Ryan DickeyPhoto by Ryan DickeyPhoto by Ryan Dickey

Brown {C- B- Ru- D-}: The pigmentation of the skin is black to rich brown and the mask is light brown with some orange overcast. The eyes are dark but with some pigment reduction: juveniles tend to have dark garnet colored eyes that darken as they reach maturity. The coat coloration is a shade of burnt brown, with orange to yellow banding on either side of the principle coloration.

Photo by Ryan DickeyPhoto by Steve HalfpennyPhoto by Ryan Dickey

Cinnamon {C- bb ruru D-}: The pigmentation of the skin is diluted to pale brown or pink, while the mask is light and hardly discernible in some individuals. The eyes are dark but with some pigment reduction, visibly dark brown in most individuals. The coat pigmentation is liver-brown with light orange-yellow banding on either side of the principle coloration.

Photo by Ryan DickeyPhoto by Ryan DickeyPhoto by Ryan Dickey

Cinnicot {C- bb Ru- D-}: Exhibit characteristics of either Cinnamon or Apricot with co- expression in the coat coloration: containing a mixture and blending of some Cinnamon and Apricot banded spines, with amounts varying between individuals.

Photo by Ryan DickeyPhoto by Ryan DickeyPhoto by Ryan Dickey

Apricot {C- bb Ru- D-}: The pigmentation of the skin is pale brown to pink. There is either a very pale, or no visible mask and the pigmentation of the eyes is greatly reduced, appearing red.  The coat is orange with some brown overcast and the bandings on either side of the principle coloration are off-white or cream.

Photo by Kelly HartPhoto by Chelsey KennedyPhoto by Ryan Dickey

The Blue-Cream Dilutions


Blue {C- B- ruru dd}: This coloration is mostly predicted from the coloration of blue-fawns. The pigmentation of the skin would be expected to range from black to brown with grey overcasting.  The eyes are dark but with some pigment reduction, visibly blue in some individuals.  The coat coloration of the mask is silvered and the spine banding have reduced color intensity and appear light grey or silver; the banding on either side of the principle coloration are off-white. The ears are notably softer and often fold.

Photo by Ryan DickeyPhoto by Ryan DickeyPhoto by Ryan Dickey

Blue-Fawn {C- B- Ru- dd}: Exhibit characteristics of either blue or fawn with co- expression in the coat coloration: containing a mixture of some blue banded spines and some fawn banded spines, with amounts varying between individuals.

Photo by Ryan DickeyPhoto by Rebecca CowellPhoto by Ryan Dickey

Fawn {C- B- Ru- dd}: This coloration is mostly predicted from the coloration of Blue-Fawns. The pigmentation of the skin should be diluted to pale brown to pink.  The eyes are assumed to be dark with notable pigment reduction.  The coat coloration of the spine banding have reduced color intensity and are yellow in appearance; the banding on either side of the principle coloration are beige or off-white.

Photo by Ryan DickeyPhoto by Ryan DickeyPhoto by Ryan Dickey

Silver Cinnamon {C- bb ruru dd}: The pigmentation of the skin is brown with grey overcast.  The eyes are dark with notable pigment reduction, visibly blue in some individuals and occasionally with brown-burgundy overcast.  The coat coloration of the mask, if it is visible, is silver and the spine bandings have reduced color intensity and appear light gray or silver, which gain more brown overtones as they reach maturity; the bandings on either side of the principle coloration are beige or off-white.

Photo by Ryan DickeyPhoto by Ryan DickeyPhoto by Ryan Dickey

Silver-Cream {C- bb Ru- dd}: Exhibit characteristics of either lilac or cream with co- expression in the coat coloration: containing a mixture of some lilac banded spines and some cream banded spines, with amounts varying between individuals

Photo by Ryan DickeyPhoto by Ryan DickeyPhoto by Ryan Dickey

Cream {C- bb Ru- dd}: The pigmentation of the skin is pink in appearance.  The eyes are red.  The coat coloration of the spine bandings is pale yellow or off-white, with off-white bandings on either side of the principle coloration.

Photo by Ryan DickeyPhoto by Ryan DickeyPhoto by Ryan Dickey

Inheritance of Coat Color in African Pygmy Hedgehogs

Dark Gray Pinto Baby Hedgehog

Ryan is a guest writer, and his views and opinions do not necessarily reflect those of Atlantis Hedgehogs. He has years of experience with coat color genetics, experience with hedgehogs since 1995, and began studying their color genetics in 2001. He earned his degree from Oklahoma State University, College of Arts and Sciences, Department of Microbiology and Molecular Genetics.

A Quick Introduction

Some of you might be familiar with my research in hedgehog genetics from ten years ago, which I removed from the internet due to the harassment and threats that I received from a small and core group of individuals in the hedgehog hobby who didn’t want a differing opinion from the recognized standard. My goal was only to share what I had found from years of personal experience in color breeding (dogs, mice, gerbils, guinea pigs, and finally hedgehogs). I don’t believe in recreating the wheel, and mammalian color genetics are not a new thing.

I have been asked to share my research with the world again, and I am going to remain foolishly optimistic that after ten years of radio silence, I won’t be met with the same attacks. What follows is a personal research study that I performed over the course of seven years. I don’t make any claims and never have of the certainty of these findings (the sample sizes are relatively small for research purposes, and I didn’t have every color available at all times); I believe in the scientific method and trust the numbers. I used these genotypes to color breed my hedgehogs for many years with great success. I only hope that others might find this information helpful too.

Inheritance of Coat Color in African Pygmy Hedgehogs (12-30-2008)

Ryan N Dickey (B.S. From Oklahoma State University: College of Arts and Sciences, Department of Microbiology and Molecular Genetics)

ABSTRACT
                The objective of this study was to provide standard and accurate tools for predicting color inheritance in the hybridized pet African hedgehog.  This required identifying and defining coat color classes by means of test-crosses and maintaining detailed records of phenotype features, as well as establishing standard and recognized coat color loci via utilization of classic comparative genomics.  The presumptive color classes and modes of inheritance were analyzed using classic genetic methods by collecting phenotype data from multiple test-crosses and the application of Χ2 analysis to determine the probability of random correlation to the hypothesized allelic relations and modes of inheritance. There were a total of 229 hedgehogs involved in this study (14 out-stock breeders and 215 offspring produced of which 52 were kept as breeding stock). The original breeding stock was selected from blood-lines originating in six states in the U.S. (Alaska, Kansas, Missouri, New Mexico, Ohio, and Oklahoma). The study introduces a new perspective on the color classes and implicates seven loci responsible for the predominant coat colors and patterns identified within the hedgehog fancy: C— albinism (recessive), B— brown dilution (recessive), Ru— brown/orange dilution (semi-dominant), D— dilution (recessive), Rn— roan (dominant), Sn— snowflaking or white flecking of the coat (recessive), and S— white spotting (dominant).

INTRODUCTION

                The attention to coat color genetics in pet African hedgehogs is a considerably recent occurrence; with hedgehogs still being new arrivals in the pet hobbyist scene.  Furthermore, the views on hedgehog colors have changed considerably throughout their time as a pet, and have always varied between different breeders and organizations. Some of these discrepancies were due to the confusion created by the hybridization of two different species in the creation of the pet hedgehog (presumably the White-Bellied hedgehog and the Algerian hedgehog, although it could have been two regionally distinct subspecies of white-bellied hedgehogs) .

                Upon the hedgehog’s arrival as a pet in the United States, the colors were viewed as being very simplistic: possessing an agouti-like pattern of banding and with only black and brown colorations (given various names by different groups: Salt-and-Pepper, Agouti, Standard, Chocolate, Cinnamon etc.) and a few color patterns, such as albinism, snowflaking (pattern of solid white spines mixed into the coat), and white spotting (Kelsey-Wood, 1995; Vriends, 1995; Wrobel, 1997). During the late nineties and into the next century the views of hedgehog colors progressed to very complicated systems, and strict color standards were created; most breeders also came to agree that hedgehogs were not agouti colored (or that they should not be described as such from a marketing perspective, in order to avoid suggesting that there was only one color variety) and ventured to explain the banding patterns as a result of different color genes interacting (Means-Burleson, 2003; Smith, 2004; International Hedgehog Association, 2006).

                Many breeders still use their own methods to describe the inheritance of the various colors, shades, and patterns seen in this interesting pet, however, the system that is accepted by mainstream breeders of the International Hedgehog Association (IHA) is the creative formula designed by Bryan Smith of HedgehogCentral.com.  This formula is fairly simplistic, utilizing a format of only two loci (the White-Bellied color set, and the Algerian color set) with several alleles and primes to explain a plethora of traits (Smith, 2004). Unfortunately, this formula does not lend accurate predictions for most crosses, as is evident from test-cross data gathered within this study. The objective of this research is to apply standard concepts of coat color genetics to pet African hedgehogs— providing a more familiar system and accurate tools for predicting color inheritance.

METHODS AND PARAMETERS

                This research complied with animal welfare regulations as outlined by the United States Department of Agriculture (USDA) and the Animal and Plant Health Inspection Service (APHIS) and was carried out within a USDA licensed facility (Class A: animal breeder) as is required for breeding exotic animals (Hedgehogs: four or more breeding females not exempt from USDA licensing).  The study was performed over the span of seven years. Hedgehogs used in the study were selected for optimizing the color diversity available within the pet hedgehog and were obtained from multiple lines in various locations in the U.S. (with origins in Alaska, Kansas, Missouri, New Mexico, Ohio, and Oklahoma): there were 14 out-stock breeders involved in this study and 215 offspring produced from 76 litters, 52 of which were kept back as breeding stock. The data collection methods consisted of test crosses, detailed records of coat, skin, and eye colorations, and high resolution photographic records of litters.

Classifying Phenotypes

                Preliminary research of the data gathered from the test-crosses was used to organize the colors into categories once clear independent modes of inheritance were observable. This was necessary since a foundation for the study was absent due to contradicting information on hedgehog colors from the current resources.

                The banding patterns observed within the study show clear signs of an agouti-like pattern in the distribution of the pigments.  From the tip of the spine moving towards the base: the spine is initially without pigmentation (appearing white or off-white), as pigmentation begins it is a tan-orange or beige hue that fades or melds into the center banding pigmentation, which can be either black, brown or orange (depending on the hedgehog’s base-color) the pigmentation then fades out towards the base of the spine with some tan-orange or beige colorations visible before another region without pigmentation. The greater the expression of the outside tan-orange coloration, the lighter the center coloration of the band will be; the pigmentation of the skin also seems to be controlled by the level of agouti expression

                For instance, a black hedgehog with low agouti expression will exhibit dark skin pigmentation and black center bands on the spines of the coat with narrow rust-colored areas on either side of the band. However, a black hedgehog on the other end of the spectrum with high agouti expression will have lighter skin pigmentation and the spine bandings will be mostly washed out to dark brown (near black) with less discernable boundary between the tan outside colorations and the darker center colorations. The variability of the agouti expression is random and causes some difficulty in regards to classifying the coat color phenotypes due to a considerable amount of overlap that it creates between the different shades of hedgehog colors.

                This effect can be further complicated by the action of the ruby-eyed (apricot or orange) gene acting on a black hedgehog. The ruby-eyed gene effects hair (spine), eye color, and skin color, but is independently variable on each . e.g. a black hedgehog with low agouti expression and the ruby-eyed effect could have a dark chocolate appearance with dark eyes, coupled with dark skin. An effect commonly referred to as having the Algerian trait in the hedgehog fancy. Other Algerian traits are a dark mask, cheek-patches, and/or forehead bands. These traits are individually inherited, and do not directly correlate with any base color grouping. The ruby-eyed gene can provide more notably golden colored cheek patches when present.

                The preliminary investigation of the phenotypes suggests that there are six fundamental color phenotypes present in the pet hedgehog. The nomenclature assigned to these colorations are in line with commonly accepted hedgehog color names and are as follows: Gray (black agouti), Cinnamon (liver agouti), Brown (brown agouti), Apricot (orange agouti), Chocolate (black-brown agouti), and Cinnicot (liver-orange agouti). Familial patterns observed indicate that gray and cinnamon are allelic while the semi-dominant and variably expressive brown and apricot colorations are the result of an epistatic relation with another locus– this is likely the divide between the two different species that were hybridized. This provides two base colors from which the other colors and patterns are derived: Gray and Cinnamon.

                This was a promising find given that these two phenotypes acting as the basic colorations of the coat is a common occurrence amongst many other mammals (Bowling, 2000; Case, 2003; Little, 1967; Griffiths, 2004; Searle, 1968).

The Six Fundamental Colors of African Hedgehogs Described

Gray: The wild-type coloration of the pet hedgehog. The pigmentation of the skin ranges from black to brown in appearance (correlating to the expression of the agouti pattern) with black eyes and a dark mask on the face; like the skin, the mask also ranging from black to brown. The coat colorations are typically black with tan-orange bandings on either side of the principle coloration.

Cinnamon: The pigmentation of the skin is diluted to pale brown or pink, while the mask is light and hardly discernible in some individuals. The eyes are dark but with some pigment reduction, visibly dark brown in most individuals. The coat pigmentation is liver-brown with light orange-yellow bandings on either side of the principle coloration.

Brown: The pigmentation of the skin is black to rich brown and the mask is light brown with some orange overcast. The eyes are dark but with some pigment reduction: juveniles tend to have dark garnet colored eyes that darken as they reach maturity. The coat coloration is a shade of burnt brown, with orange to yellow bandings on either side of the principle coloration.

Apricot: The pigmentation of the skin is pale brown to pink. There is no visible mask and the pigmentation of the eyes is greatly reduced, appearing red.  The coat is orange with some brown overcast and the bandings on either side of the principle coloration are off-white or cream.

Chocolate: Exhibit characteristics of either gray or brown with co-expression in the coat coloration: containing a mixture and blending of some black banded spines and some brown banded spines, with amounts varying per individual.

Cinnicot: Exhibit characteristics of either cinnamon or apricot with co- expression in the coat coloration: containing a mixture and blending of some cinnamon banded spines and some apricot banded spines, with amounts varying between individuals.

                These six color classes each have a diluted variant, except for gray and brown; of which the dilute variants produced in this study all died before seven weeks of age. Whether these fatalities are an inherent quality of the dilution gene with the gray coloration or due to unknown factors within this study could not be determined in the scope of this study.  There are no publications regarding blue colorations in pet hedgehogs.

                The dilute colorations have been assigned the following names for this study: Blue (dilute gray), Silver-Cinnamon (dilute cinnamon), Fawn (dilute brown), Cream (dilute apricot), Blue-Fawn (dilute chocolate), and Silver-Cream (dilute Cinnicot).

The Six Dilute Colors of African Hedgehogs Described

Blue: This coloration is mostly predicted from the colorations of blue-fawns since individuals of this coloration did not survive to maturity. The pigmentation of the skin would be expected to range from black to brown with grey overcastting.  The eyes are dark but with some pigment reduction, visibly blue in some individuals.  The coat coloration of the mask is silvered and the spine bandings have reduced color intensity and appear light grey or silver; the bandings on either side of the principle coloration are off-white. The ears are notably softer and often fold.

Silver-Cinnamon: The pigmentation of the skin is brown with grey overcast.  The eyes are dark with notable pigment reduction, visibly blue in some individuals and occasionally with brown-burgundy overcast.  The coat coloration of the mask, if it is visible, is silver and the spine bandings have reduced color intensity and appear light gray or silver, which gain more brown overtones as they reach maturity; the bandings on either side of the principle coloration are off-white.

Fawn: No fawns were produced in this study and like blue this coloration is mostly predicted from the colorations of blue-fawns. The pigmentation of the skin is diluted to pale brown to pink.  The eyes are assumed to be dark with notable pigment reduction.  The coat coloration of the spine bandings have reduced color intensity and are yellow in appearance; the bandings on either side of the principle coloration are off-white.

Cream: The pigmentation of the skin is pink in appearance.  The eyes are red.  The coat coloration of the spine bandings is pale yellow or off-white, with off-white bandings on either side of the principle coloration.

Blue-Fawn: Exhibit characteristics of either blue or fawn with co- expression in the coat coloration: containing a mixture of some blue banded spines and some fawn banded spines, with amounts varying between individuals.

Silver-Cream: Exhibit characteristics of either lilac or cream with co- expression in the coat coloration: containing a mixture of some lilac banded spines and some cream banded spines, with amounts varying between individuals

                 The three remaining color patterns of the pet hedgehog have been well documented by numerous color breeding enthusiasts, although no standard genetic symbols have been assigned to them. They are the albino (no pigment), pinto (a white spotting trait), and snowflake (white ticking) patterns.

                The only information added during this study to the classification of these three traits pertained to the snowflake pattern.  A second, seemingly non-allelic snowflake pattern was discovered; it was labeled as roan due to its similarity to the coat color pattern of the same name in other captive bred mammals.  The roan pattern is mostly indistinguishable in appearance from the snowflake pattern, but shows a different mode of inheritance and interaction with the dilution trait.

                With the twelve basic color phenotypes classified (the six fundamental colors and the dilute variants), an acting definition of the colors was available and the remainder of the research was focused on assigning appropriate standard genetic symbols and the analysis of breeding records to determine the accuracy of the findings regarding the allelic relations and modes of inheritance.

Establishing Loci and Assigning Standard Nomenclature

                The primary method utilized in this study to determine the loci responsible for the phenotypes observed (i.e. the most appropriate allele symbols) was comparative genomics of coat, eye, and skin pigmentation to find the best fitting homologous loci from other mammals. This is based on the long practiced principle that mammalian coat color genetics share key features and can be represented with a standardized set of loci and symbols (Searle, 1968). Working from this concept, the initial coat color genetics reviewed for potential phenotypic homologies were those of mice: the color genetics of mice are the best studied and have shown a strong correlation to findings in other captive bred mammals (Griffiths, 2004). Other species investigated for color homologies were the domestic dog, cat, and horse.

                The largest contributing resource for identifying loci that possessed potential homologous expressions with the phenotypes and modes of inheritance seen in hedgehogs was the Mouse Genome Informatics web site (http://www.informatics.jax.org), which contains a plethora of data from databases of multiple contributing projects [Mouse Genome Database (MGD), Gene Expression Database (GXD), Mouse Tumor Biology (MTB), Gene Ontology (GO), and MouseCyc]. The MGI Phenotype Search engine was utilized as a proficient tool in identifying numerous potential phenotypic homologies between mice and hedgehogs pertaining to mutations in coat pigmentation.

                The hedgehogs’ brown coloration corresponded highly with the expression of the classic B-locus: coat diluted to brown and eye pigmentation slightly reduced. With the wild-type black coloration showing a dominant mode of inheritance to brown, the alleles were assigned as B for gray and b for cinnamon.

                The B-locus is considered to be one of the principle loci common to many mammals and is utilized nearly universally as a standard symbol for black-brown dilution (Griffiths, 2000; Nicholas, 2003; Searle, 1968). The brown/apricot trait shows co-expression with both the gray and the cinnamon phenotypes. It also showed greater reduction of eye pigmentation than brown dilution, diluting the eyes to dark garnet (nearly black) in young brown offspring and to ruby-red in apricot offspring.

                Phenotype search inquiries of the MGI databases suggested many possible homologies, but without any definite matches. The various Ruby-Eyed dilution alleles found in mice show similar characteristics to the hedgehog brown/apricot trait, particularly Hps3coa-7J. There were also many correlations with variants of the Pink-Eyed dilution gene, or Oca2p; with Oca2p-J showing the greatest similarities amongst the P-alleles. However, none of these show a semi-dominant pattern of expression, nor do any match all or most of the characteristics observed in the brown/apricot trait of the pet hedgehog. Furthermore, none of the other species researched in this study contained any obvious homologies to this coloration, the closest being orange in the domestic feline or the sable in the domestic canine, which show co-expression in the coat (Case, 2003; Ruvinsky, 2001). However, in domestic felines this co-expression is a mosaic pattern of a sex-linked trait due to X-inactivation, and the brown/apricot trait of hedgehogs shows no signs of sex-linked inheritance or sex-influenced expression; and neither orange nor sable generate any effect on eye coloration.

                The closest match in appearance, noted from photographic record, is the Cocoa-7-Jackson coloration of mice mentioned previously. From this mutuality, the genetic symbol chosen for the brown/apricot trait in hedgehogs was Ru (ruby-eyed), to denote the phenotypic similarities in expression to a gene of the ruby-eyed series present in mice.  These genetic symbols (B and Ru) were adopted and utilized with the observed modes of inheritance to generate a hypothesized set of genotypes for the six chief colorations of hedgehogs:

Gray B/- ; ru/ru
Chocolate B/- ; Ru/ru
Brown B/- ; Ru/Ru
Cinnamon b/b ; ru/ru
Cinnicot b/b ; Ru/ru
Apricot b/b ; Ru/Ru

                The dilute variants of the primary coat colorations exhibit shared heritability, i.e. lilacs and creams can be bred from blue-fawn lines if they are carriers of the cinnamon gene; indicating that the same allele is responsible for dilute forms of all of the basic colors.  The dilution trait reduces the pigmentation overall, with effect in coat, skin, and eye coloration, producing a general silver-fawn appearance.

                There are many dilution traits in domestic bred mammals. Most are represented with the genetic symbol D, which can be found in canines, felines, equines, and mice with very similar expression (Bowling, 2000; Case, 2003; Little, 1967; Ruvinsky, 2001; Searle, 1968). The dilution trait in hedgehogs shares many of the characteristics of these common dilution traits, and search inquiries of the MGI Phenotype Search engine yielded supporting results, thus this common genetic symbol is used in the study to refer to the dilution trait in hedgehogs.

Blue B/- ; ru/ru ; d/d
Blue-Fawn B/- ; Ru/ru; d/d
Fawn B/- ; Ru/Ru; d/d
Silver Cinnamon b/b ; ru/ru; d/d
Silver-Cream b/b ; Ru/ru; d/d
Cream b/b ; Ru/Ru; d/d

                The remaining color patterns are not included in the results of this study, as they have either already been well described in previous literature, or there was not ample data available secondary to the rarity of the patterns. They are included in this study to provide standard gene symbols, which they are lacking in the breeding hobby, and to introduce the previously unknown roan trait.

                The roan trait shows a simple dominant mode of inheritance.  It is expressed as white spines uniformly and randomly mixed into the coat of the hedgehogs over the back, without affecting colored areas on the face or legs. A similar roan pattern exists in horses, where the standard gene symbol Rn is used (Bowling, 2000). Inquiries of the MGI Phenotype Search engine also showed correspondence with the Rn-locus and roan hedgehogs. This gene has been selected as the candidate gene for roan coloration in hedgehogs, and the standard genetic symbol applied within the parameters of this study.

                The roan trait has shown another interesting feature in this study. Roan hedgehogs that were born expressing the pattern in their baby coat have only produced offspring that do not roan-in until they lose their baby coat (assuming they inherit the roan trait), while those that did not roan-in until they lost their baby coat have only produced offspring that are born expressing the trait in their baby coat (assuming they inherit the roan trait). This pattern is suggestive of a genomic imprinting pattern and could be utilized as a tool for distinguishing roans from snowflakes. The roan gene has also shown possible linkage to the blue-fawn dilution gene, although ample data is not yet available to confirm this [data not shown].

                The snowflake pattern is well described in much of the current and older literature on pet African hedgehogs.  Bryan Smith, one of the first hedgehog breeders to thoroughly describe and study the trait suggested that snowflake was a recessive (Smith, 2004).  Data collected in this study supports his earlier findings [data not shown]. There are many different varieties of white ticking and roan patterns in mammals, and without any further defining features, it was not possible to identify one that fit best as a potential homologous trait to the pattern seen in hedgehogs; the genetic symbol Sn (for snowflake) is used in this study to represent the locus of the snowflake gene.

                There is another, and far more rare, variant of the snowflake pattern known as white, in which the coat is almost entirely without pigmentation, presenting only a few colored spines in the forehead region. There is currently little information available on the inheritance of the white phenotype.

                White spotted, or pinto, patterned hedgehogs have been thoroughly described.  The trait is expressed as colorless patches that appear on any area of the hedgehog at birth, although it is more commonly present around the rump. Both skin and hairs will be colorless in the affected areas. The trait is described as having a dominant mode of inheritance (International Hedgehog Association, 2006; Means-Burleson, 2003).  Many domestic mammals use the genetic symbol S to represent white spotting patterns (Griffiths, 2000); the same symbol is used in this study.

                Albinism is described in older hedgehog literature and remains one of the most identifiable colorations in the pet.  It has a simple recessive mode of inheritance, and is expressed as a complete absence of pigment, affecting the entire hedgehog. The genetic symbol C has long been used to refer to albinism in domestic animal breeding and is considered one of the standard symbols (Griffiths, 2000; Nicholas, 2003; Searle, 1968). It was, therefore, adopted in this study for the genetic symbol for albinism in hedgehogs.                 The resultant color genome of the pet African hedgehog from the findings listed above is C/-; B/-; Ru/-; D/-; Rn/-; Sn/-; S/-. The hedgehogs used in the research were genotyped from pedigree records and testcrosses assuming the above hypothesis. Data sets collected from test-crosses focusing on the B, Ru, and D loci were organized by loci and then analyzed using Χ2 equations to determine the accuracy of the predictions of this study.

RESULTS

The B Locus

CROSS No. Observed No. Expected Χ2 Value Probability
BB x (BB, Bb, bb) 84 : 0 100% : 0 N/A No variance
Bb x Bb 10 : 5 11.25 : 3.75  0.56 0.30<p<0.50
Bb x bb 32 : 27 29.5 : 29.5 0.42 0.50<p<0.70
bb x bb 0 : 30 0 : 100% N/A No variance

The Ru Locus

CROSS No. Observed No. Expected Χ2 Value Probability
ruru x ruru 27 : 0 100% : 0 N/A No variance
Ruru x ruru 50 : 46 48 : 48 0.17 0.50<p<0.70
Ruru x Ruru 14 : 38 : 3 13.75 : 27.5 : 13.75 12.41 * 0.001<p<0.01 *
RuRu x ruru 4 : 0 100% : 0 N/A No variance
RuRu x Ruru 5 : 1 3 : 3 2.67 * 0.10<p<0.20 *
RuRu x RuRu No data available

The D Locus


CROSS
No. Observed No. Expected Χ2 Value Probability
DD x (DD, Dd, dd) 148 : 0 100% : 0 N/A No variance
Dd x Dd 16 : 4 15 : 5 0.27 0.50<p<0.70
Dd x dd 9 : 8 8.5 : 8.5 0.267 0.50<p<0.70
dd x dd 0 : 3 0 : 100% N/A No variance

CONCLUSION

                The data failed to reject the hypothesis except for the hypothesized co-dominant mode of inheritance of the Ru-locus. The data, instead, indicates that the ruby-eyed dilution trait demonstrates a dominant mode of inheritance and exhibits a high occurrence of variable expressivity tending towards the median.

The production of full brown or apricot offspring only from crosses where homozygous combination is a possibility does suggest that homozygosity of the ruby-eyed dilution allele increases the probability of full brown/apricot dilution. However, according to the data obtained, homozygosity of the Ru allele does not dictate complete expression, and the majority of hedgehogs homozygous for this allele are indistinguishable from those that are heterozygous.

There was also one sample analyzed that produced expected values of less than five, rendering the Χ2 results inconclusive on the basis of conventional statistical practice. However, the cross was testing for co-dominant expression of the ruby-eyed trait, and the results correlate with those mentioned above.

Given these findings the genotypes of the principle colorations of pet African hedgehogs can be revised in the following manner to demonstrate the lack of complete dominance of the Ru allele.

B/- ; ru/ru ; D/- Gray
B/- ; Ru/- ; D/- Chocolate > Gray or Brown
b/b ; ru/ru ; D/- Cinnamon
b/b ; Ru/- ; D/- Cinnicot > Cinnamon or Apricot
B/- ; ru/ru ; d/d Blue
B/- ; Ru/- ; d/d Blue-Fawn > Blue or Fawn
b/b ; ru/ru ; d/d Silver-Cinnamon
b/b ; Ru/- ; d/d Silver-Cream > Silver-Cinnamon or Cream

LITERATURE CITED

Some homology data for this paper were retrieved from the Mouse Genome Database (MGD), Mouse Genome Informatics, The Jackson Laboratory, Bar Harbor, Maine.  <http://www.informatics.jax.org > . Jul. 2008.

Bowling A.T., and A. Ruvinsky, ed. The Genetics of the Horse. New York: CABI Publishing, 2000.

Case, Linda P. The Cat: Its Behavior, Nutrition & Health. Ames: Iowa State Press, 2003.

Griffiths, Anthony J. F., et al. “Gene Interaction in Coat Color of Mammals” An Introduction to Genetic Analysis. New York: W. H.   Freeman, 2000. NCBI.
<http://www.ncbi.nml.nih.gov:80/books/bv.fcgi? >. Nov. 2004.

International Hedgehog Association. Divide, CO. 2006. <http://www.hedgehogclub.com/ > . Jun. 2008.

Kelsey-Wood, Dennis. African Pygmy Hedgehogs As Your New Pet. Neptune City: T.F.H. Publications, 1995.

Little, Clarence C. The Inheritance of Coat Color in Dogs. New York: Howell Book House, 1967.

Means-Burleson, Antigone. The Hedgehog Primer: Everything you need to know about the basic care of pet African Hedgehogs. Instantpublisher.com, 2003

Nicholas, F. W. Introduction to Veterinary Genetics. 2nd ed. Oxford: Blackwell Publishing, 2003.

Ruvinsky, A, and J. Sampson, ed. The Genetics of the Dog. Wallingford: CABI Publishing, 2001.

Searle, A. G. Comparative Genetics of Coat Color in Mammals. London: Logos Press Limited, 1968.

Smith, Bryan. Hedgehog Central. 2004.
<http://www.hedgehogcentral.com/colour.shtml > . Jun. 2008

Vriends, Mathew M. Hedgehogs. Hauppauge, NY: Barron’s Educational Series, Inc., 1995. Wrobel, Dawn. The Hedgehog. New York: Howell Book House, 1997.