The Genetics of Hedgehog Colors

Introduction:
      Hedgehog colors are not different from those of other mammals. Several years of working through the modes of inheritance and interactions of the principle genes responsible for the expression of hedgehog colors have determined that the main mutated loci in hedgehogs might include the common loci C, B, and D, along with some less common ones, such as the ruby-eyed locus (genetics symbol = Ru).
      For the readers who are less familiar with genetic concepts and terminology, I have included a basic genetics page on this site (Genetics Tutorial). If you have any questions or suggestions regarding the information presented herein, then please feel free to send an e-mail to atlantishedgehogs@yahoo.com.
 --  Ryan N. Dickey, student in the department of Microbiology and Molecular Genetics at Oklahoma State University.

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The C Locus:
      One of the colors that seems to confuse the largest number of breeders is albino. It is not that the genetics of albinism are complex (they're actually quite simple), but many people just do not understand what albinism is; I have found that the best way to explain the albino phenotype is to think of it as the mystery color. Albinism is the result of an error at the beginning of the pigment producing chain, therefore, regardless of the other color genes an albino might have, it will still be completely colorless (pictured on the right) because the biological pathway for color production never starts. So in other words albinos are still genetically some color, but because of the albinism mutation that color, whatever it may be, will never be seen, ergo, the mystery color.
      The wild-type allele of the albino locus, C, allows normal pigment production to initialize. This is the dominant allele of this locus, so if at least one of the wild-type alleles is present a hedgehog's color will express as 'instructed' by their other color genes. The recessive allele of the albinism locus, c, is the mutant allele that does not produce the proper enzyme to begin pigment production, so a hedgehog with two c alleles at the albino locus will be albino.
For an example I will use three different genotypes, all of which are genetically instructed to be brown by the B and Ru loci:
C/C ; b/b ; ru/ru => Cinnamon
C/c  ; b/b ; ru/ru => Cinnamon
c/c   ; b/b ; ru/ru => Albino

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The B and Ru Loci:
      As is seen in the coat colors of the majority of mammalian species, there are two main colors in hedgehogs from which the other colors are derived (i.e. the base colors)— black and brown (or chestnut and cinnamon). The switch between these two colors is controlled by a single locus (one gene). This gene has acquired a few different names throughout the world of coat color genetics: the black gene, the black-brown gene, and the brown dilution gene. It is represented by the letter B; its two variants are the Black allele (B) and the brown allele (b). As the capitalization indicates, black is dominant to brown. This means that a hedgehog will be black unless it inherits the brown allele from both of its parents. In terms of it's genotype, a hedgehog that inherits a genotype of either B/B or B/b will be black, while one that inherits the genotype b/b will be brown.
  B/B => Chestnut (black)
  B/b => Chestnut (black)
  b/b => Cinnamon (brown)
      Matters would be far more simplistic if the black-brown gene were the only gene in control of the principle colorations seen in hedgehogs, but, alas, now things get a bit more complicated, for there is another. It is the Ruby-Eyed dilution gene, represented by the genetic symbol Ru. It is basically another black/brown switch, but with brown being a semi-dominant allele. For this reason the capitalized is the opposite from the black/brown locus: ru is black and Ru is brown. In terms of the genotype ru/ru is black while Ru/ru and Ru/Ru are at least partially brown, with Ru/Ru having an increased probability of producing an entirely brown hedgehog.
      However, the Ru/Ru browns are not the same shade as the b/b browns; they are closer to shades of sepia and orange than the b/b browns, which are closer to shades of red and earth-toned brown.
      And now for the fun part, combining these two different genes. Epistatically, the B and Ru loci exhibit co-expression. Meaning that one will not hide the effects of the other, but they will instead both express to varying degrees. However, when the two brown genotypes are combined (b/b ;Ru/-) the hedgehog is greatly diluted (including the eyes) and will be orange in appearance. The genotypes are as follows, B/-;ru/ru is a black hedgehog, B/-;Ru/- is at least a partially sepia colored hedgehog, b/b;ru/ru is a brown hedgehog, and b/b;Ru/- is at least a partially orange colored hedgehog.
      I know that all of this can be difficult to follow, so, in an attempt to neatly summarize everything I've covered up to this point, I drew a pretty picture (using high-resolution photographs of the spine bandings). The range table below shows how the variably expressive genes that interact with the chestnut and cinnamon phenotypes create a continuous gamut of colors.

Note that these colors do not look the same on all monitors and cannot be assumed to be true.

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The D Locus:
      The dilution gene dilutes eumelanin (black/brown) to silver-blue and pheomelanin (tan/orange) to yellow-cream. This type of dilution most frequently operates by creating clumping of the pigment granules, which causes light to reflect differently, thereby changing the appearance of the color without actually changing the type of pigment.
      Unfortunately, the dilution gene does not always work the way that we would like it to in hedgehogs. Like most of the colors in domestic hedgehogs, it has not been selectively bred to increase its desired expression. Dilutes are the colors that I have spent the most time working on in my own breeding program; already I have gotten colors that supposedly do not exist, such as dilute cinnicot (pictured on the left), which have a mixture of lilac and cream colored spines. Getting colors like these without utilizing in-breeding techniques requires one to be very selective, not only in the stock that they keep back, but also in the stock that they acquire from other breeders. This is not only because the dilution gene in hedgehogs has not yet been enhanced through selective breeding but also because the blue dilution gene is recessive. In order for a hedgehog to be a dilute, it must inherit the gene from both of its parents; which may or may not have been dilutes themselves. Hedgehogs with the genotypes D/D or D/d are not dilutes, while those with the genotype d/d are.
      There are dilute variants of each of the principle colors, however, producing blues (dilute blacks: B/-;ru/ru;d/d) seems to be problematic. The picture to the right is of blue colored spines on a young blue amber hedgehog (B/-;Ru/ru;d/d), which seems to be the only way to get a glimpse at what blues should look like. Unfortunately, and although it has not yet been confirmed, at this time, the data seems to suggest that blues may have severe health problems that lead to runting and death before they reach maturity (around 7 to 8 weeks), with some babies possibly dying before birth. One dilute color being fatal is not an uncommon problem with the dilution gene and is observed in various other animals as well.

Note that these colors do not look the same on all monitors and cannot be assumed to be true.

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The Rn Locus:
      Roan is a term that describes a pattern of white hairs mixed into a colored coat. It could technically be used to describe the snowflake pattern as well (which is discussed in the next section). In fact, roan hedgehogs are indistinguishable from snowflakes on appearance alone, however, roans are the result of a simple dominant gene, while snowflake is produced by a recessive gene. The genetics symbol Rn is used to depict the roan gene, where the genotype Rn/- produces roan and rn/rn does not.
      Roans seem to be far more rare than snowflakes, and could be the result of a new mutations that has occurred since the initial breeding stock was imported (or just the result of them masquerading as snowflakes all along). One of the most interesting finds encountered with this pattern is that it appears to be linked to the dilution locus. Gene linkage occurs when two loci are close to each other on the same chromosome, preventing regular cross-over between them and therefore greatly reducing the frequency at which they are independently assorted.
      If the roan locus truly is linked to the dilution locus then in the genotype the two linked alleles would be written together: e.g. Rn d//rn d would be a dilute roan (like the blue amber roan pictured on the left), and any roan offspring from an individual with this genotype would be known to be at least carrying the dilution allele. In other words, the two linked alleles from the different loci would pass on as if they were a single allele.
      Another interesting find with the roan pattern is that there seems to be genetic imprinting involved in the process of determining when the offspring will express the gene. As with snowflakes, some roans are born expressing the pattern in their baby coat, while other roans are born without the expression and do not show it until they get their adult coat. Unlike snowflakes, where it is random chance determining whether a baby will express the pattern in their baby coat or not until after quilling, roans show a distinct pattern of when they will 'roan-in', depending on the pattern expression of their roan parent.

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The Sn Locus:
      Having an abundance of white (un-banded) spines mixed into a hedgehogs coat (at approximately a 1:1 ratio with the normal banded spines) is a pattern that has been dubbed snowflake by breeders, a term that has been accepted as the official name for the pattern by the IHA (visible in the picture below of a tawny snowflake hedgehog). The common snowflake gene, represented by the genetics symbol Sn, has a simple recessive mode of inheritance in hedgehogs. That is to say that individuals with the genotype Sn/Sn and Sn/sn are not snowflake, while those with the genotype sn/sn are. This means that a snowflake x snowflake cross will always yield snowflake offspring, although some might not 'flake-in' until they get their adult coat, i.e. after quilling, which can occur later than twelve weeks of age. It is also true that in order for a hedgehog to be a snowflake it has to inherit the snowflake allele from both of its parents.
      There is another pattern that is similar to snowflake, and that seems to be somehow genetically related; it is referred to as white. Whites are basically the same as snowflake but they have almost no banded spines at all (with only about ten or less on their forehead), and some can actually be completely without any banded spines (the latter pattern is usually called double-white).
      Whites have generated a great amount of confusion amongst breeders. While there has not been any conclusive research done involving these patterns, I have developed a theory to match the inheritance patterns that have been observed based on data that I have obtained from other breeders who have bred primarily for whites. At this time it appears as though recessive snowflakes have the potential to be whites but for the presence of a dominant suppressor gene. A suppressor gene is a gene that prevents another from expressing; i.e. a white is a snowflake without the suppressor gene. This concept has been outlined in the tree-diagram below.

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The S Locus:
      The pinto pattern is a variably expressive trait, with co-dominant inheritance. It is a type of white spotting, and is represented by the genetics symbol S, where the genotype S/S and S/s yield the pinto pattern and s/s does not.
      The degree to which the spotting expresses is extremely variable, where some pinto individuals may have only a tiny spot of pink skin on their side with a couple of white spines there, and others can be nearly completely white. The black pinto pictured to the right has the average amount of spotting that is commonly seen.
      The spots are a complete decoloration of areas on the hedgehog which can be either segmental or generalized. So not only will the hairs or spines of the spot be white, but the skin underneath them will be pink. The spots can appear anywhere there is skin, including the face and ears and any area over the backs and legs, even on the tail. The only area I have yet to see affected by pinto spots are the eyes, but that's not to say that it isn't a possibility.

Conclusion and Summary:
      The initial methods of this preliminary study have been completed; however, there are many aspects of hedgehog coat color genetics that are still unclear. The table below outlines all of the alleles thought to exist along with their hypothesized function and mode of inheritance; based on the data collected.

      In order to further summarize the information that has been presented on this page I have designed a flow-chart that displays a simplified explanation of the working theory of the series of biochemical pathways involved in producing the colors that we see in hedgehogs. Keep in mind that this flow-chart is not intended to be anything more than an educational outline; the order of the genes in the tree, although not entirely arbitrary, is not intended to be representative of the true pathways.