CHROMOSOME ABERRATIONS IN ANIMALS 



673 



tion of salivary-gland chromosomes (Kaufmann, 1941a). This method 

 permits detection not only of rearrangements, but also of their types and 

 proportions, and of the total number of breaks involved. The results 

 are given in Table 9-6. 



Table 9-6. Comparison of Frequencies of Induced Chromosome Breaks Result- 

 ing from Continuous and Discontinuous X-ray Treatment of Males 



(Kaufmann, 1941a) 

 (No errors are furnished for the percentage of breaks, since the distribution of the 

 number of breaks is not given by a Poisson series; 1 X 3000 r and 1 X 4000 r refer to 



a Data from Bauer, 1939b. 



b Includes data from Bauer, Demerec, and Kaufmann, 1938. 



These findings have been interpreted as indicating that breaks produced 

 by irradiation of the mature spermatozoon do not participate in the 

 formation of new rearrangements until after the sperm has entered the 

 egg in fertilization; but, as will be discussed subsequently, this conclusion 

 can apply only to the viable class of aberrations that are available for 

 diagnosis by genetical or cytological techniques. 



Experiments to determine the effect of differences in temperature on 

 the production of rearrangements have given conflicting results. The 

 earlier studies of Papalashwili (1935) and Mickey (1939), which indicated 

 that low temperature during irradiation results in a higher frequency of 

 chromosomal rearrangements than high temperature, were not confirmed 

 by the extensive work of Muller (1940) and Makhijani (1949), in which 

 similar frequencies of translocations between the second and third 

 chromosomes of D. melanogaster were obtained when temperatures as 

 different as 4.5 and 37.5°C were applied either at the time of irradiation 

 or at the time of fertilization. In another series of experiments (Kauf- 

 mann, 1946b, 1948a), it was found that there was no significant difference 



