LIFE PROCESSES IN CAPTIVE GRAY RATS 55 



occurred in these rats, similar to that found in the mouse 

 (Dunn and Thigpen, '30), but no genetic tests of this assump- 

 tion were made. Later the hair in some individuals had a 

 distinctly brownish tinge, but inbreeding through several gen- 

 erations did not change the coat color to that of the non-agouti 

 brown or chocolate rat. 



Routine examination of newborn litters of the thirteenth 

 generation disclosed three individuals in which the eye color 

 seemed somewhat lighter than that normal for gray rats. 

 Rearing these rats, which belonged in a litter cast when the 

 mother was 16 months old, revealed a second mutation in the 

 strain, ruby-eyed dilute. Two more of these mutants appeared 

 in a later litter from the same parents, making a total of five 

 mutants in thirty-four young. Normal young from these 

 litters were reared and used for breeding. As expected, a 

 number of ruby-eyed dilutes appeared among their descend- 

 ants in later generations. Matings of these mutants with 

 ruby-eyed descendants of the first rats of this type, which 

 were discovered by Whiting (Whiting and King, '18), gave 

 only ruby-eyed dilute young. These two mutations from un- 

 related gray stocks were due, therefore, to the same recessive 

 gene which dilutes pigmentation in the eyes as well as in the 

 coat. 



A third mutation, albinism, was discovered in two rats of 

 the fourteenth generation through the color of the eyes at 

 birth. These mutants were members of the fifth litter cast 

 when the mother was 14 months old. There were no other 

 mutants among her forty-five offspring. Sisters of this fe- 

 male mated to other males produced only gray young, but 

 albinos were found among their descendants during several 

 succeeding generations. 



The next mutation found, curly (Cu), was a type not pre- 

 viously recorded in rats, although subsequently two mutations, 

 phenotypically similar but genetically different, were discov- 

 ered; kinky (k) by Feldman ('35), and curly 2 (Cu 2 ) by 

 Gregory and Blunn ('36). Curly is a dominant mutation that 

 affects hair structure, not its color. It eliminates or greatly 



