Two New Color Factors of the Guinea Pig

A fifth member of the albino series of guinea pigs, dark dilution, ck, has been identified. It causes distinctly less dilution of black pigment than does the previously known dilution factor cd, although very little less dilution of red. It is recessive to intensity (C) but imperfectly dominant over light dilution (cd), red eyed, non-yellow dilution (cr) and albinism (ca). The allelomorphic series, C, ck, cd, cr, ca, is the longest yet reported in mammals. A factor (f) reducing red to a yellow, which fades later to cream and even white, but intensifying black, has been found among the descendants of a single mating. It behaves as a unit recessive to its normal allelomorph (F) and is transmitted independently of the albino series. It is suggested that the intensification of black is a secondary consequence of a primary dilution of red and is due to a partial release from a competition between the processes of black and red color production, and is thus parallel to certain effects, previously described in the albino series. This factor represents a new class of color factors in rodents. Its closest parallels seem to be found in certain color varieties of the hog.