EXPERIMENTAL STUDIES OF THE INHERITANCE OF 

 COLOR IN MICE. 



PART 1. 



THE FACTORS PRODUCING COLOR IN MICE. 



In the coat of the common house mouse {Mus musculus) three pigments are 

 recognizable, yellow, brown, and black. No connecting intergradations of color 

 between these three types are visible. The inheritance of these colors and of 

 their distribution, both qualitatively and quantitatively, has been the object 

 of many investigations and is the principal feature of the present paper. 



All mammalian color has been found due to melanin pigment. Riddle 

 (1909) has discussed the process of the formation of melanin pigment and states 

 that all chemical evidence supports the idea that melanin pigment is the 

 product of an oxidation process. The substances (chromogens) on which the 

 oxidizing agents (enzymes) act were found to be tyrosin and certain related 

 aromatic compounds. It has been further shown that tyrosinase-like ferments, 

 which occur widely distributed in the organism, act as oxidizing agents, thus 

 producing melanin compounds. Furthermore, it has been proved that at least 

 artificial melanins may pass through a series of colors before arriving at the 

 final stage of oxidation. In such series the earlier stages of oxidation give lighter 

 colors than the later ones. 



Cu^not (1903) advanced an hypothesis to explain the formation of color 

 by the interaction of a chromogen substance and an enzyme. He called the 

 chromogen the general factor for the production of color, C, and supposed that 

 in albinos this chromogen substance is lacking, thus making it impossible for 

 color to be formed. Riddle, however, states that the nature of the chromogen, 

 it being very widely distributed throughout the organism, is such that any 

 theory postulating the absence of this substance would be chemically absurd. 

 Gortner (1912), however, finds evidence that chromogens in insects may be of 

 restricted distribution, thus forming color patterns. 



At present it is impossible to decide finally between the explanation offered 

 by Cu^not and that suggested by Riddle. We shall have to await further 

 chemical evidence to determine whether the albino does or does not lack the 

 oxidizable substance or substances necessary for pigment production.* 



If we assume that there is only one enzyme present to act as an oxidizing 

 agent, we must assume for it as many different degrees of activity as are re- 

 quired to explain the occurrence of the various colors known to mendelize (three 

 in mice, yellow, brown, and black). If we assume that a different enzyme or 



*A recent paper by Keeble and Armstrong (1912) has shown that in Primula sinensis 

 lack of chromogen seems to be the cause of albinism, thus favoring the original hypothesis 

 of Cudnot. 



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