20 



THE INHERITANCE OF COLOR IN MICE. 



If we consider, in addition to tin.' 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 F x 

 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 



