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)
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).
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.
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.
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
|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|
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|
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.
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<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.