20 



THE INHERITANCE OF COLOR IN MICE. 



If we consider, in addition to the above result, those obtained in a similar 

 cross by other investigators, we may construct the following table : 



*SeeBateson (1903). 



In the cross between the heterozygous pigmented animals obtained in Fi 

 and pure albinos, where equality of pigmented and albino young is expected, 

 the following result has been obtained : 



As this cross has been largely neglected in my experiments the numbers are 

 extremely small. If, however, a table is made showing the work of other inves- 

 tigators, larger and more valuable results are obtained : 



All investigators have found that when albino mice are crossed inter se, 

 only albino young are produced. Albinism is, then, a recessive character. 

 Cuenot (1903) considered albinism due to the loss of the general color factor 

 C (chromogen), but for the reasons given by Riddle this interpretation seems 

 of doubtful validity. 



As before stated, mammalian pigment results from the action of an enzyme 

 or enzymes upon a chromogen substance. Albinos are formed from colored 

 varieties by the loss or restriction of one of these substances. Present chemical 

 evidence discredits the possible loss of the chromogen ; the enzyme or enzymes 

 remain to be considered. Albinos probably lack one or more of these. If 



