Genie Control of Development 395 



processes, and we may safely assume that the same type of changed 

 genie action accounts for both effects. 



All these and comparable cases (which Griineberg considers also 

 as spurious pleiotropy) contain some information on genie interplay. 

 In the a+ pigment in Ephestia it is safe to assume that kynurenine is, 

 or can be, produced in all cells or not be produced in the case of aa 

 action. However, it will be oxidized further into pigment only in cells 

 which are competent for it (if we use this term, as before, in this 

 wider sense). "Competent" means here an independently determined 

 condition, probably of cytoplasmic differentiation, produced in one of 

 the ways discussed above, but certainly in the end under genie control. 

 Thus pattern pleiotropy shows us the interplay between a genically 

 controlled specific reaction and other, independent ones, controlling a 

 patterning process by means of cytoplasmic "stratification." This cyto- 

 plasmic diversification may act by producing different degrees of 

 polyteny, according to Henke's very interesting work (Henke and 

 Pohley, 1952) on Lepidoptera scales (see III 5 A a), where both the 

 type and amount of pigmentation are dependent upon the degree of 

 polyteny. If this process were combined with the patterning process 

 of the aa pigment, an interesting series of genie interactions would be 

 visible. (All of them have been individually discussed in previous 

 chapters.) 



A third type of pleiotropy, which we might call "dichotomic 

 pleiotropy," is found when some primary reaction of a mutant, usually 

 an inhibitory one, is of such a generalized type that it affects the 

 entire organism simultaneously according to the reactivity of its parts. 

 A deficiency in a growth substance, for example, may affect every 

 growth process, but differently according to its independently deter- 

 mined features. The Minutes in Drosophila may serve as an example. 

 Small size and weakness are simple effects. Abnormal shape of wings 

 and abnormal venation are interactions of the same primary defect 

 with the individual steps of independently determined wing develop- 

 ment. Shortening of bristles and roughness of eyes may be rather 

 simple interferences with growth processes. (We mentioned earlier, in 

 III 5Cb, the relation of roughness of eye facets to definite biochemical 

 deficiencies, which, however, cannot be considered the direct cause.) 

 Abnormalities in the genital region may involve more intricate proc- 

 esses within an imaginal disc and their interactions and compromises 

 through embryonic regulation. 



Still another type of pleiotropy might be called "interference 



