339 



On the Change that Takes Place in the Chromo- 

 some in Mutating Stocks. 



Roscoe R. Hyde. 



Two new eye mutations, tinged and blood have appeared in my 

 cultures of the fruit fly that throw light upon the question as to the nature 

 of the change that takes place in the chromosome when a new character 

 appears. Both mutations show typical sex-linked inheritance, consequently 

 they are expressions of changes in the X chromosome. Both mutants give 

 the same linkage values when measured with other sex-linked characters. 

 When measured with yellow body color a linkage of 1.2 results; with minia- 

 ture wings 33; with bar eyes 44. Morgan has described three sex-linked 

 eye mutants, white, eosin and cherry, which give the same linkage values. 

 Consequently, we now have five sex-linked eye mutants, namely, white, 

 tinged, eosin, cherry and blood, which give an increasing color series from 

 white to the bright red of the wild fly. A study of their linkage relations 

 shows that they either lie very closely together on the X chromosome or that 

 they are but different modifications of the same gene. The two possibilities 

 involve the question of the origin of mutations as well as the fundamental 

 make-up of an hereditary factor. 



Mendel evidently thought of something in the germ cell that stood for 

 round (R) and something that stood for wrinkled (W) and that these two 

 things could not coexist in the same gamete. That is, (W) is allelomorphic 

 to (R). 



The origin of mutation in the light of the above assumption would 

 seem to depend upon the splitting up of more complex hybrids — the bring- 

 ing to the surface of units already created. Evolution in the light of such 

 a conception would seem to depend upon the shifting together of desir- 

 able units. 



Bateson viewed the matter in a different light. He knew of the origin 

 of new forms by mutation. He postulated a definite something in the germ 

 cell that stands for the character, as for example (T) which stands for the 

 tallness in peas, which when lacking makes the pea a dwarf (t). In other 

 words, instead of two separate factors he regards the tallness and dwarfish- 

 ness merely as an expression of the two possible states of the same factor, — 



