CHROMOSOME ABERRATIONS IN ANIMALS 



667 



side and Lea, 1945a). At higher dosage levels the frequency increases 

 more rapidly than the first power of the dose. This deviation from 

 linearity has been attributed to the dominant-lethal effects of deficiencies 

 and asymmetrical exchanges involving two or more breaks, which are 

 produced with higher frequencies at higher doses (Fano and Demerec, 



< 



Id 



CD 



u_ 

 O 



LlI 



o 



LlI 

 CL 



10 20 30 40 50 60 70 80 90 100 110 120 130 



DOSAGE, r 



500 1000 



1500 2000 2500 3000 

 DOSAGE, r 



3500 4000 4500 5000 



— ■ ADULT WASPS FAILING TO EMERGE 



DROSOPHILA EGGS OF OREGON R STOCK FAILING TO 



HATCH (SONNENBLICK) 



DROSOPHILA EGGS OF OREGON R STOCK FAILING TO 



HATCH (DEMEREC AND FANO) 



ADULT DROSOPHILA OF OREGON R STOCK FAILING 



TO EMERGE (DEMEREC AND FANO) 



Fig. 9-13. (a) Relation between X-ray dose and the production of single breaks in 

 neuroblasts of Chortophaga. (From Carlson, 1941a.) (b) Dose-frequency relations 

 for dominant lethals in Drosophila and Habrobracon. (Data of Demerec and Fano, 

 1944; Sonnenblick, 1940; Heidenthal, 1945.) 



1941; Demerec and Fano, 1944; Lea and Catcheside, 1945; cf. also the 

 study of Bauer and Lerche, 1943, on the midge, Phryne fenestralis). 

 Another line of evidence that the frequency of the single-break type of 

 dominant lethal in Drosophila is directly proportional to dose has been 

 obtained by Bauer (1942), in a study of the distortion of the sex ratio 

 resulting from X-ray treatment of spermatozoa carrying a ring-X chromo- 

 some. In studies of Habrobracon (Heidenthal, 1945; cf. A. R. Whiting, 



