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PHYSIOLOGICAL GENETICS 



It baa already been stated I bai the production of phenocopies in 

 Drosophila succeeded only if the temperature shock was applied 

 at a definite time in development, the sensitive period. It could 

 be shown (Goldschmidt, 1935a) (1) That some of the phenotypes 

 could he produced only during a rather short period; e.g., the 



Fig. 3a. 

 FlG. 3. — a, »0-wings at different temperatures; b, vg male wings at 32.9°C. 

 (1st col.) and at 34° (2d and 3d col.). (From Riedel, 1934, Arch. Entwicklg- 

 mech. 132, Figs. 12, 13.) 



type with scalloped wings can be produced only during a short 

 period preceding pupation; (2) that other phenocopies may be 

 produced over a rather considerable stretch of time in develop- 

 ment, provided that a sufficient stimulus is provided; (3) that 

 the sensitive periods of different phenotypes may overlap; (4) 

 that the sensitive periods ceteris paribus are different in different 

 races. Table 3 gives the results for a few types in percentage 

 of obtained phenocopies in one experiment. 



