Crossingover in Drosophila 



337 



viated form in the table from which one group of females which 

 showed the same effect as the other two has been omitted. The 

 first two sets of bottles show no significant difference in the 

 crossover value between the control and the X-rayed females. 

 The third and fourth bottles, however, show a significant differ- 

 ence between the control and X-rayed females both in the case 

 of the separate groups and in the case of the series as a whole. 



The counts of crossovers and noncrossovers from all of the 

 experiments may be added together. It is then found that the 

 difference between the crossover values of the control and X- 

 rayed females for eggs laid during the first six days is 2.03 times 

 the probable error and that for eggs laid during the second six 

 to eight days of egg laying the crossover value of the X-rayed 

 females is less than that of the controls by 28.37 times the prob- 

 able error of the difference. 



The fourth series of experiments shows that the effect of the 

 X-ray treatment even when that treament lasts only for 3 min- 

 utes and 17 seconds is apparent in the crossover values over a 

 period of approximately six days. This result tends to show 

 that the X-rays do not directly affect the process of crossingover 

 but that they produce in the chromosomes or the nucleus gener- 

 ally a condition which inhibits crossingover. 



CROSSOVER VALUES— FOURTH SERIES OF EXPERIMENTS. 







X-rayed 











Control 









■ 









m 











Group 



of Pai 



oneross- 

 overs 



Cross- 

 overs 



Crossin 

 over 



Ph 



O 



oncross- 

 overs 



Cross- 

 overs 



Crossin 

 over 



Diff. 

 E. diff 



o 



















FIRST BOTTLES 



I 11 103 39 27.5 9 351 156 30.8 1.4 



III 7 55 21 27.6 4 154 64 29.4 1.4 



I-III 26 203 76 27.2 19 843 358 29.8 1.27 



SECOND BOTTLES 



I 



10 



95 



30 



24.0 



9 496 



216 



30.4 



2.0 



III 



7 



37 



14 



27.5 



4 202 



92 



31.3 



.8 



I-III 



24 



173 



59 



25.4 



18 1012 



466 



31.5 



2.77 











THIRD 



BOTTLES 









I 



8 



294 



21 



6.78 



9 433 



149 



25.7 



9.6 



III 



6 



155 



20 



11.4 



4 222 



108 



32.7 



7.2 



I-III 



21 



624 



64 



9.29 



18 958 



362 



27.4 



12.85 



