CROSSINGOVER IN DROSOPHILA 



167 



clear. The females which laid the first ten day brood recorded 

 were the offspring of a female which had hatched at 31.5°C, 

 No. 430. The first, No. 468, itself hatched from a tube kept at 

 31.5°C. The second, No. 474, hatched from another tube kept 

 at 22°C. Both were heterozygous for black-purple-curved and 

 were back-crossed to a black-purple-curved male from stock. 

 The results follow : 



TABLE 10 

 b — pr — c 



Pi parents hatched at 31.5° 



The percentages show the characteristic increase in crossing- 

 over among the offspring of the heat-hatched females, while that 

 hatched at 22°C. gives a percentage even lower than normal. 

 The effect of the temperature is shown, therefore, not to be 

 inherited. 1 



Second brood data 



The analysis of the extent of the temperature effect now 

 leads to the second question proposed above, namely, is the 

 entire output of eggs of a female hatched at a high temperature 

 affected or only those laid during the first ten day period? The 

 answer to this question has resulted in a corollary of consider- 

 able theoretical importance, and therefore the results will be 

 given in some detail. The method for testing this point is very 

 simple. After the Fi females backcrossed to males of the mu- 

 tant stock have been allowed to lay in one bottle for ten days, 



1 The fact that both the control and the heat values given in table 10 are 

 significantly lower than those given in table 8, suggests that possibly high tem- 

 peratures may result in a lower rate of crossingover among the offspring, though 

 that low rate can be stimulated proportionally by exposure of the parents to heat. 

 The effect of heat continued for many generations should be further investigated. 



