386 Action of the Genetic Material 



fications, inhibitions, enhancements, suppressions. It is safe to say that 

 all of them will fit one or the other explanation of interaction men- 

 tioned before and just enumerated. Therefore, no more examples 

 are needed than those already used incidentally in the discussion of the 

 various problems of action of tlie genie material. 



But there are also a number of special investigations of the 

 problem which are of two types: one deals with morphological 

 characters, which means that the interpretation can be only a more or 

 less indirect one. The other deals with chemical differences, which 

 permit a rather exact interpretation. Only a few examples of each type 

 will be mentioned in order to show that they lead, in a general way, 

 to conclusions concerning genie action of the same types as discussed 

 before. 



An interesting attack upon the problem is that made by Dunn and 

 Coyne (1935) and Dunn and Mossige (1937), because they use one 

 genie effect which must be supposed to affect many others, quanti- 

 tative changes in speed of development. The previously mentioned 

 Minutes in Drosophila have a retarding effect upon development 

 (Brehme, 1939, 1941). It is true that Minutes are frequently defi- 

 ciencies and are suspected of being of heterochromatic nature. But 

 for our present discussion they may serve as models of one possible 

 type of genie action. Dunn and Coyne used the delaying effect in 

 descending order for the Minutes, Mw — Mb — Mz — Mh — MI2. These 

 were combined with other mutant effects, for example, eye size. In 

 such combinations the eye size was reduced in the presence of 

 Minutes and in degree, corresponding to the retarding effect of the 

 series of Minutes. Whatever the genie action which reduces eye size 

 (see III 5 C a bb), the interplay with the independently determined 

 and affected rate of development and its orderliness point to actions 

 and interactions involving some phase of the kinetics of genie action. 



Another example which deals with eye reduction, this time by 

 Bar, is Hersh's work (1929). It is not a combination effect with a 

 known genie activity which is studied here, but rather the modifying 

 effect upon one quantitatively measurable genie action (eye-facet 

 numbers) by other mutant loci in the same chromosome which, as 

 such, affect eye structure, eye color, and wing properties. All these, 

 individually and combined, affect facet number, much or little, 

 positively or negatively. One of these modifiers is vermilion, the 

 chemical action of which is the prevention of kynurenine synthesis. 

 In view of the results of Chevais (see III 5 C a bb), it cannot be 

 excluded that the absence of kynurenine in the developing eye stalk 



