Referate. 



Morgan, T. H. Faclors and unit characters in Mendelian heredity. Amer. 



.Nat. 47 1913. S. .5—1(1. 

 Castle. W. E. Simplification of Mendelian formulae. Amer. Nat. 47 



1913. S. 170—182. 

 Morgan, T. H. Simplicity versus adequacy in Mendelian formulae. Amer. 



Nat. 47 1913. S. 372—374. 

 Emerson, R. A. Simplified Mendelian formulae. Amer. Nat. 47 1913. 



S. 307-311. 



These papers contain suggestions and criticisms regarding changes in 

 the present system of recording Mendelian formulae. Morgan points out 

 that although genetists have repeatedly repudiated any intention of regarding 

 a unit character as the product of a single unit factor, confusion between the 

 two terms still persists. In Mendel's original work no such trouble existed 

 because Mendel did not meet with a complex case of inheritance. He de- 

 signated the gametic representatives of segregating characters bj' capitals and 

 small letters, but his a was as much a reality as his A. When Bateson 

 found that rose comb and pea comb were both dominant to single comb in 

 fowls, however, the system broke down and caused the elaboration of the 

 presence and absence hypothesis. The letter p henceforth meant simply the 

 absence of a germinal unit P, and the letter r the absence of a germinal 

 unit R. The fact that P and R together brought about the production of 

 the walnut comb was not in the least disturbing. 



Morgan finds, however, that even the system of Bateson is confu- 

 sing when dealing with complexities such as he has found in the ej'e color 

 of Drosophila ampelophila. For example, certain eye colors have been represented 



as follows: t. t n j- 



P \ red 



p Y vermilion 



P v pink 



p V orange 



Now the presence and absence hypothesis, he says, implies that some- 

 thing is lost from the original germplasm PVO when the vermilion pVO 

 arises. „The vermilion color is supposed to be the product of what is left 

 when this something (called P) is lost. It is not supposed on this hypothesis 

 that the vermilion factor alone is responsible for the vermilion color, for it 

 is hypothetically only a part of what is left when something (P) is lost. 

 Yet it is the identification of the vermilion factor with the vermilion eye- 

 color that the opponents of Mendelism seem anxious to impute to the Men- 

 delians." 



