26 



THE INHERITANCE OF COLOR IN MICE. 



The above-described fluctuations in the density of pigmentation are to a 

 certain extent hereditary. Thus cream-colored mice crossed i77ter se have a 

 greater number of cream-colored than of deep-yellow young. So, too, from 

 deep-yellows crossed together the deep-yellow young preponderate, but cream- 

 colored young may occur as well. 



We may now consider the result of crosses between intense animals pos- 

 sessing the factor D and animals with the modified or "dilute" condition d. 

 If homozygous intensely pigmented animals (DD) are crossed wtih dilute 

 animals (dd) only intense young (Dd) are formed in Fi. In my experiments 

 424 young have been thus produced, all intense, manifesting D. If these het- 

 erozygotes are crossed together we should expect in F2 the ratio 3 intense 

 to 1 dilute young. The experimental results are as follows: 



When the heterozygous intense animals are crossed back with the dilute 

 type the following results have been obtained : 



Here there is a marked deficiency of dilute animals, which is in all prob- 

 ability partly due to failure on my part to recognize as dilute certain of the pink- 

 eyed dilute animals produced during the years 1907-08. During these years 

 many matings of this type were made. In classifying the young obtained from 

 these I may have been in error. Thus if we consider the matings made since 

 1908, which should theoretically produce both dilute and intense young, we 

 should have the following results : 



Here there is an excess of dilute animals, which makes it seem probable 

 that in the matings previous to 1909, of the two types given above, I confused 

 the dilute and intense pink-eyed forms, often failing to distinguish them cor- 



