THE MUTATED GENE 



59 



chemically (poison) — further differentiation or, by lysis, destroys 

 existing tissue. Or it may be the consequence of the lack of 

 something necessary for differentiation, an insufficiency, e.g., of a 

 growth substance, a vitamin. If we use first the latter concept 

 for the sake of simplicity, we could represent the case in the form 

 of the diagram (Fig. 20). The series of wj-genes controls the 

 production of the growth substance in question which has to 

 be present at each stage of development in sufficient quantity to 



W 



q uant, wild rypejimitam^ 



10/// 

 9//I 



Nicked 



Min.2d.inst. 



. Notched 

 e it 



y 



6//I Snipped 



**■ s/n Ragged 

 m 4/u Antlered 



vm 



3/n Strap 

 EC 



?/!/ Vestig/af 



X* '/it No wing 



3-8 £3 





s^ 



s S 



■54 »t f 



«■ g 



Fig. 20. — Graphic representation of the action of the different ^-alleles upon 

 destruction of wing area. Abscissa instars; ordinate wing growth. (From 

 Goldschmidt, 1937, Univ. of Calif. Publ. Zool. 41.) 



insure normal differentiation. In the Wild type and in all 

 compounds producing the Wild type, the rate of production of this 

 substance has to be above this minimum. As the production 

 must keep pace with the normal growth of the wing Anlage, the 

 top curve in the diagram might represent as well the growth 

 curve of the Anlage as the curve of production of the growth 

 substance. As the facts of development show, the deficiency of 

 this substance begins earlier and earlier in the progressive series 

 of alleles and continues to increase almost up to the end of wing- 

 development, as shown by the continuous degeneration. The 

 curves for the production of this substance must therefore begin 

 to drop at a certain point in development and continue to do so 



