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Summary The antigenic specificities of six (1‐6) IgG allotypes of the domestic mink were tested in the sera of closely related species of Mustelidae family and distant mammalian species. It was found that allotypes 1 and 5 are ancient. Their antigenic specificities were established not only in Mustelidae, but also in other taxonomic orders of mammals. Allotypes 3 and 2 are phylogenetically younger; they were detected only in Mustelidae. Allotypes 4 and 6 appear to be unique to the domestic mink. The instantaneous evolutionary emergence of complex allotypes 4 and 6 is difficult to explain by a rapid accumulation of gene point mutations during phylogenesis. Activation in the domestic mink of those immunoglobulin genes, which are silent or poorly expressed in closely related Mustelidae, is suggested as a more plausible explanation.