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 inter 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 Fi 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- 



