-22 



I'HYSIOUUiUM. GENETICS 



a curve of the average diameters of this field on the wing after 

 heat treatment at different times as compared with the untreated 

 control-. A few further details regarding the amount of the 

 reaction may be gained from Fig. 7 to which we shall return later. 

 Similar determinations have been made for other elements of the 

 wing pattern in the same object as well as in Abraxas grosmlariata, 

 the currant moth. Some of the data will be reported later in 

 the chapter on pat tern. 



$1Y 



III 



11 



12 3 4 5 6 7 



Da\/s 



Fi<;. 8. — Superposition of a heat effect upon the dominigene effect in the 

 heterozygous zip- wing in Drosophila. Broken curve: amount of scalloping of 

 wings (classes I-V) in the controls, with genetic scalloping produced by the 

 ^-dominigenes; average grade for individuals hatching on consecutive days. 

 Full-line curve: The same line treated with temperature shock: on the third 

 day the animals are hatching in which the genetic, and the temperature effect 

 are additive. {From Goldschmidt, 1935, Z. ind. Ahstl. 69, Fig. 17.) 



It is not probable that in higher plants strictly comparable 

 facts will be met with, as developmental mechanics are so differ- 

 ent from animals. But Harder (1934) claims that flowers of 

 Petunia have a sensitive period in which the pattern may be 

 influenced by temperature and light in a definite way. 



D. Combination Effect of Gene and Phenocopy 



For our task — to prove that the processes underlying the forma- 

 tion of phenocopies are the same as those set in motion by 

 mutant genes — the following facts are of importance: Gold- 

 schmidt (1935a) treated with the method that produces scalloped 

 wings both Wild-type flies and flies that have genetically scalloped 

 wings (^-hcterozygotes with dominigenes). The result was that 

 in the latter case the genetic and the phenocopic effect were 

 added, and a more extreme scalloping was produced. Figure 8 



