GENIC INTERACTION 189 



Neurospora, bacteria, maize, mice, and so forth. The comparison of genetic constitu- 

 tions, as when nutritional requirements, sensitivities to drugs, and the like of inbred 

 strains are compared, is another approach often used. The effect of teratogens, the 

 production of phenocopies, is a method which has some merit when cautiously inter- 

 preted. Genie interactions are fundamental in the complex of interrelationships 

 involved in the realm of physiologic genetics, the genetics of expression; but genie 

 interaction (the second approach) as a deliberate method of investigation has been 

 used all too little, except for Dr. Wright's long-term studies on guinea-pig coloration 

 and hair direction. 



Relating directly to the details of this paper, pink-eyed dilute (p) in combination 

 with Light (B lt ) prevents basal dilution in the mouse, a situation somewhat analogous 

 to one mentioned by Wright. Recently we have discovered a possible interrelationship 

 between murine Polydactyly and anophthalmia. In no case, however, have we made 

 a systematic attempt to combine our mutants for study in the Wrightian manner. 

 Murine genetics during the past 30 years has placed more than enough emphasis on 

 the development and maintenance of inbred strains and on single-gene differences; 

 perhaps now more should be done to explore genie interactions. After all, as Dr. 

 Wright said at the beginning, "genie interaction ... is obviously fundamental in 

 physiologic genetics and is almost as fundamental in population genetics, including the 

 genetic aspects of the theory of evolution." Whereas he said in his introduction that 

 he was riding the two wild horses of physiologic genetics and population genetics, 

 I would like to make the observation that the one horse of physiologic genetics, tamed 

 by Dr. Wright, has been enough for me. 



Dr. Popp: Frank Moyer at Johns Hopkins University has been interested in 

 differences among pigmented granules of murine melanoblasts as regards possible 

 differences in tyrosinase in such cells; 914 information on structural differences among 

 tyrosinases of the mouse may be forthcoming in a year or two. 



Dr. Russell: Dr. Douglas Coleman at the Jackson Laboratory also has under way 

 a splendid program analyzing genetically determined differences in tyrosinases in 

 mouse skin. 213 



Dr. Yerganian: With respect to outlining the genes involved in diabetes mellitus 

 of the Chinese hamster, Cricetulus griseus, we have conducted appropriate hybridizations 

 involving symptomatic animals representing four different strains. To our surprise, 

 instead of the anticipated retention of the high incidence of diabetic animals among 

 the F x of single- and double-hybrid crosses, the frequency of symptomatic hamsters 

 was virtually nil. The syndrome 865, 866 reappeared after three and four generations 

 of brother-sister matings. We have estimated the number of genes to be two, in 

 addition to an unknown number of modifiers that control the degree of penetrance and 

 age of onset. These observations have been repeated on numerous occasions, but the 

 role of modifiers remains to be fully disclosed. 



Since diabetes failed to occur following the hybridization of symptomatic animals, 

 the role of modifiers is most perplexing. An interaction among the genes as well as 



