Genetics of Fur Color in Foxes, Emphasizing DNA Studies
A brief review of the genes controlling fox coat colors and patterns. All of this research has been conducted in the labs of others. Our lab studies coat color ONLY in dogs and cattle. Many of the photos here are taken from the web. These are not photos of foxes actually DNA tested for the coat color they illustrate, contrary to my dog and cattle webpages. This is not ideal, but since I do not do research on fox color, it's the best I could do.
The photo of a wild Red Fox, at the right, was taken years ago by Josef Schmutz. Even in the wild, fur color varies. (see drawings from a wild fur technical bulletin prepared by the North American Fur Auction.)
This webpage was mounted on April 2, 2014 and last updated on January 24, 2017 by Sheila Schmutz. firstname.lastname@example.org
The main farmed fox colors are:
The photo at the right was taken at Bill Worb Furs in Winnipeg in December 2015. The lighter pelts on the left would be shades of Blue Fox and the darker ones on the right would be Silver Fox. A glimpse of some wild arctic fox is visible below the Blue Fox. In general, ranched or farmed foxes are much larger than wild foxes.
According to the Fur Commission USA website and the US Fox Shippers Council, these colors were developed by crossing the Red Fox (Vulpes vulpes) with the Arctic fox (Alopex lagopus), as well as natural mutations that arose in foxes on farms. Keep in mind, however, that farmed fox fur is also frequently dyed when used in fur apparel.
The photo at the left shows the main three shades of wild foxes in Canada. A red fox pelt is at the bottom, a silver fox pelt is in the middle and a cross fox pelt is at the top. This photo was taken at International Fur Dressers and Dyers in Winnipeg, Manitoba in December 2015.
DNA Studies To Date
Studies in Norway in 1997 found that mutations in two genes explained several of the coat colors in foxes. These two genes interact with each other and so various combinations of alleles are possible that jointly affect the color. These genes are the agouti signal protein (ASIP) and the melanocortin 1 receptor (MC1R).
A wild Red Fox would have the genotype E+/E+, A/A. The pelt at the right was from a fox in eastern Canada, salted and stretched over 30 years ago.
The Red Fox at the right was photographed in Prince Albert National Park in December 2014. This fox has probably been fed by campers there because it sat and "posed" within a few yards of our parked car.
Standard Silver Fox
The photo at the left is from Wikipedia and depicts a "Silver Fox". The Wikipediapage on the silver fox suggests that this variant coat color arose in the wild long ago, referencing "The Imperial Collection of Audubon Animals" by John James Audobon in 1967. Wikipedia also reports that silver foxes were "native" to Prince Edward Island, Canada in the late 1800s and were subsequently farmed. But under "Domestication", it is implied that this mutation arose in farmed foxes in Russia after 1959 and was called the Siberian Fox.
The photo of this stuffed fox, at the right, was taken at the Hawood Inn in Waskesiu, in Prince Albert National Park, Saskatchewan by Sheila Schmutz. The label says "red fox", but this is clearly an atypical red fox. It is probably a "silver fox" variant. Foxes escaped from fox farms over the years so this fox could be one of those, or was a farmed fox, or could have been a descendant of naturally occurring variants of this type. This one also sees to have a rusty hue compared to the typical farmed silver fox.
A deletion in exon 1 of the ASIP gene in farmed red fox leads to a more dark pigmentation. Animals homozygous or (a/a) have the color known as Standard silver if they carry no mutant E allele. Their genotype would therefore be E+/E+, a/a. The silver fox variant phenotype is inherited as a recessive condition compared to the typical red fox.
More photos of the various color combinations are available in the original manuscript. In the nomenclature of this research study:
Farmed red fox with a mutation in MC1R changing the 125th amino acid from cysteine to arginine, are more darkly pigmented. They are said to carry the Alaska Silver allele (EA). It would seem that this allele might have been called B in the Scandinavian system.
In the nomenclature of this research study:
The gene that is involved in the color change to white in winter in the Arctic Fox is MC1R. Vage et al. (2005) discovered that when two amino acids were changed to cysteine in the extracellular portion of this gene, this seasonal color change did not occur. These changes likely affect disulfide bridges. They refer to a fox with these mutations as a "blue fox". They report this mutation as dominant. This should be an E allele, perhaps EW, but it's not clear if this allele has been named in the Scandinavian nomenclature.
The fox at the left (photo from http://true-wildlife.blogspot.ca/2010/12/arctic-fox.html) is part way through the seasonal change to white. The fox at the right, from Wikipedia, is in its winter white coat.
They further say that the offspring of an arctic fox (E+/E+, a/a) and a Red Fox would be called "Golden Island".
White, Homozygous Dominant Lethal
Farmed arctic fox can occur in a white coat color all year round. This white is considered to be inherited as a dominant to the blue variant that does not change to white in winter (see above). It is also considered to be lethal when homozygous. Yan et al. (2014) found this mutation occurred in the KIT gene, eliminating the entire exon 12. Photo above of a white fox pup and a blue fox pup, courteously provided by Dr. Yan.
photo from Johnson et al. 2015
Another mutation has been identified in the KIT gene. This one eliminates exon 17 in farm bred red foxes with a platinum phenotype. Like the mutation described above, this mutation is also lethal when homozygous causing embryos to die. The mutation is a single base pair change at the beginning of exon 17 which causes it to be skipped.
Furthermore the authors of this study state: "The platinum phenotypeis allelic to several other whitespotting phenotypes in foxes, including marble, white face and Georgian white. Although mutations for these phenotypes have not been found yet, identification of the platinum mutation strongly suggests that these white-spotting phenotypes are also caused by mutations in the KIT gene."
Color Loci Shown to Affect Fur Color in Foxes
|A||ASIP||Melanistic (more black) when a/a, "silver"|
|E||MC1R||EA = darker pigmentaiton, "Alaska silver"; wild type has been called both E and E+|
|W||KIT||WP = platinum or "white"|
Links to Related Sites
for further information contact:
Sheila M. Schmutz, Ph.D., Professor
Saskatoon, Canada S7N 5A8