White Spotting in the Fox

Abstract

(1) Platinum silver, the platinum color phase in silver foxes, first brought to attention by Norwegian breeders, appears to have arisen independently by mutation in at least three instances in the United States and Canada. (2) The platinum character is characterized by a dilution in tone of the black pigment in the coat, accompanied by white markings, particularly on the face and neck, which are usually fairly extensive. (3) Platinum behaves in inheritance as a dominant which is lethal when homozygous. This is supported by the fact that only heterozygous individuals are known and the further fact that the litter size is reduced in platinum by platinum matings. Completely white pups which are dead at birth or die shortly after are occasionally found. These are taken to represent individuals of the homozygous dominant class which have survived longer than is usual or by chance have been found. (4) A phenotypically similar white-face mutation is found in the silver fox. This differs from platinum in that the tone of the black is intense, rather than dull, particularly on the ears, elbows and other places where it is not so much intermixed with white or white-banded hairs. This difference in intensity of the black is particularly diagnostic in the young pups, the platinums at that stage being bluish, the white-face silvers definitely black. (5) Inheritance of white-face is similar to that of platinum in that the dominant homozygote is lethal, litters from heterozygote x heterozygote matings are reduced in size, and completely white pups are occasionally found in such matings. (6) The data are insufficient to settle definitely whether the genes determining them are independent or allelic. The latter hypothesis is adopted provisionally as being the simpler, and the symbols w+, W and WP are adopted for standard silver, white-face and platinum, respectively, in order of dominance. The white-faces in this allelic series are denominated Strain A. (7) It is suggested that the relation of white-face and platinum to silver might be explained by a progressive chromosome deficiency. (8) Another strain of white-faced, or white-marked, foxes is very similar to Strain A in phenotypic appearance and seems again to have the same characteristics of inheritance. The breeding data, however, indicate that it is not an allele of Strain A, but that the gene, or possibly deficiency, responsible for it involves a different chromosome pair. This second strain we have called Strain B. (9) Strain A and Strain B appear to be supplemental in their action, as foxes carrying genes for both have the white markings of the face and neck considerably extended. Commonly the white extends up on the ears in a characteristic fashion which has led to naming this type of foxes "white-ears." (10) Blue eyes occasionally occur in each of the types of foxes discussed in this paper. The blue may invade the iris of one or both eyes (heterochromia iridis) or one or both eyes may be completely blue. In general, the greater the extent of white on the face the greater the likelihood of blue in the eyes. For this reason blue eyes occur with greater frequency in the white-ear type than in the others. The white-ear foxes also appear to be of a more nervous temperament as indicated by their actions. (11) Platinum and white-marked are not sex-linked and appear to have equal phenotypic expression in both sexes.