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Scientific Proceedings (130) 



crossingover to cross the heterozygous females with a recessive 

 male, which in this case would be white-eyed and miniature- 

 winged, in order that the daughters may also show the crossover 

 and noncrossover classes. The experiments to be described were 

 designed primarily to test for nondisjunction and for that reason 

 the females were mated to males with the dominant character 

 red-eyed so that the exceptional sons and daughters could be 

 recognized. This did not of course affect the character of the 

 regular sons and it is from counts of these that the crossover 

 values have been determined. No attempt has been made to cor- 

 rect the data for double crossingover. 



The first series of experiments in which the effect of X-rays 

 on crossingover was tested were those of our third series of 

 X-ray experiments. Each group of females was treated only 

 once but the X-ray dose was different in the different groups. 

 The females were mated immediately after the treatment to wild- 

 type males. The X-rayed and control females were allowed to 

 remain in the first bottles for six days and in the second bottles 

 for eight days. The F x were counted in the bottles until 

 eighteen days after the parents were placed in the bottles, the 

 temperature of the incubator being kept between 73° and 76° F. 

 In the first bottles there was no significant difference between the 

 crossover values of the control and X-rayed females. On the 

 other hand in the second bottles there was a significant decrease 

 in the crossover value of the X-rayed females whenever a suf- 

 ficient number of F x were obtained to give a significant result. 

 The totals for all the experiments of the series show a difference 

 between the control and X-rayed females of 14.97 times the 

 probable error and a difference of 9.31 times the probable 

 error between the first and second bottles of the X-rayed 

 females. The experiments also show that the crossover value 

 decreases as the X-ray dose increases. 



In the fourth series of experiments, the second in which the 



w M 



crossover value was investigated, the females, — , were all 



W e m 



the daughters of one white-eyed female. The X-ray dose was 

 practically the same in all cases but the duration of the treatment 

 was varied from 3 minutes and 17 seconds to 20 hours and 20 

 minutes. The X-rayed and control females were transferred to 

 new bottles every three days. The results are shown in an abbre- 



