MORGAN, COAT COLORS IN MICE 93 



Crosses between the Sport and Albinos 



Sport I bred to a white female gave three grays with white belly and five 

 grays with gray belly in one litter; and in a second litter, one gray with 

 white belly and one gray with gray belly. Sport III bred to a white 

 female gave four grays with white belly and one gray with gray belly. 



In all, therefore, there were eight grays with white belly, and seven 

 grays with gray belly, which is approximate equality and confirms the 

 view that the sports used were heterozygous. None of the whites used 

 appear to have contained yellow. 



Crosses between F 1} Hybrid Sports and Yellows 



One of the hybrid white-bellied mice (F x ) crossed to yellow gave four 

 yellows, two grays with white belly, three grays with gray belly, one black 

 and two whites. One of the hybrid grays with gray belly crossed with 

 yellow gave two grays with gray belly, one golden agouti and two yellows. 



Crosses between F lf Hybrid Sports 



Two hybrid grays with white belly, bred together, gave three grays with 

 white belly. They may appear to have been pure, but the number of 

 young is too small to make this certain. One hybrid gray with gray 

 belly, bred to gray with white belly, gave three grays with gray belly and 

 one golden agouti with gray belly. 



New Type of Gray with a Yellow Belly 



As ordinary gray mice grow older, the hair on the ventral surface often 

 becomes yellowish. In some of the many offspring descended from 

 crosses between the wild sports and domesticated mice, individuals have 

 appeared again and again with the whole ventral surface distinctly yel- 

 lowish in color. Some of those with deeper color have been paired and a 

 race produced most members of which have a deep yellow belly replacing 

 the white belly in the sport. This color is not due to age, for while it is 

 true that it often becomes yellower as the mice grow older, I have found 

 young mice, three weeks old, with a distinct yellow belly. 



Under the microscope, the yellow hairs of the belly are seen to have a 

 yellow outer end and a black inner part. The hair may be said to be 

 ticked with yellow and black. 



The introduction of yellow into the white belly suggests the possibility 

 that the yellow is the result of crosses with ordinary yellows, but I can 



