yo Outline of Genetics 



is necessary to the success of this vital function. On such a basis, 

 the lethal would be regarded as a factor rather than a determiner, 

 and would of course be thrown into the complementary factor 

 class. The present writer does not believe that genes should be 

 called factors simply because there theoretically may exist other 

 genes necessary to the production of the character in question; 

 but holds the view that the term "determiner" should be main- 

 tained so long as only one of the effective genes in the set has been 

 identified. In the case of the lethals, however, there have been 

 discovered in the same organism (the fruit fly) a number of genes, 

 the absence of any one of which will bring the lethal effect. It 

 is reasonable, therefore, to regard these as composing one or more 

 complementary sets governing the performance of certain vital 

 functions. 



(The student may wonder how it is possible to identify lethal 

 factors when their absence simply brings death, an unrecordable 

 phenotype in the population. This will be understood later when 

 the subject of "linkage" is discussed.) 



It should be realized that genes, be they factors or deter- 

 miners, may at times have more than one role. The A factor in 

 corn, mentioned above, interacts with R and C in a complementary 

 set for the production of aleurone color in the grain. A also has 

 an effect in producing pigment in the vegetative parts of the plant. 

 The R and C factors in stocks (Saunders 6) are a complementary 

 pair for the production of colored flowers. R, C, and a third 

 factor, H, must all be present for there to be hairs on the leaves. 

 Such phenomena support the belief that the gene is not a "vital- 

 istic" unit endowed with a specific function in connection with a 

 single plant character, but rather is of the nature of many chemi- 

 cals, the presence of which will inevitably affect the course of 

 more than one type of reaction. 



LITERATURE CITED 



1. Bateson, W., Mendel's laws of heredity. Cambridge. 1909. 



2. CzAPEK, P., and M. E., Biochemie der Pflanzen. Jena. 1913. 



3. East, E. M,, and Hayes, H. K., Inheritance in maize. Conn. 

 Agric. Exper. Sta. Bull. no. 167. pp. 142. ph. 25. 191 1. 



