The Nature of Coat Color Differences in Mink and Foxes

OAT colors in laboratory mammals such as the mouse, rat, guinea pig and C rabbit have long been used in genetic studies involving the physiology and transmission of genes.Horses, cattle, swine, sheep, goats and other domestic animals also present an array of different coat colors, but with the exception of the use of a particular color or color pattern as a breed marker, differences in pigmentation probably have little or no economic value in these forms.The situation is just the reverse with regard to the fur bearing animals raised in captivity; the value of the pelt is considerably influenced by color phase.Although color has always been one of the most important factors in determining pelt value, the fur trade became color phase conscious to a marked degree with the appearance of the first platinum silver fox pelts on the New York market in 1940.Since that time, mutant colors in mink and foxes have been in great demand.The studies reported here deal with some quantitative and qualitative differences in pigmentation of the pelage of the silver, platinum and pearl color phases of the red fox (Vulpes vulpes L.= V .julva species), and the dark, platinum and pastel color phases of the mink (Mustela vison Peale and Beauvois).The mutant color phases mentioned result from single gene substitutions, and so far as is known, all of the individuals contributing fur samples differed from their respective standard ranch-bred color phases only at the mutant locus indicated.The main objective of the study was to isolate some of the links in the chain of events which intervene between the gene and its end point.This information should have value in studies of gene physiology.Three methods of approach to this problem have been considered: (1) histological aspects of guard hair pigmentation, (2) quantity of melanin pigment production as determined by weight, and (3) measurement of pigment granule length.Coat color in mammals is generally attributed to melanins, organic compounds containing nitrogen, usually dark in color, and characterized by chemical inactivity.Observations such as the persistence of color in mutant spots or areas, and in transplantation experiments indicating the local pro-* The cost of the accompanying plates is paid by the GALTON AND MENDEL MEMORIAL FUND.