No. 583] BOLE OF EXVIEOXMKXT IX DROSOPHILA 395 



Non-cross-over BAb Crossover RN 

 gametes WN gametes WAb 



The percentage of crossing over as calculated from 

 the abnormal classes (males and females) is 2.1. 



In order to obtain further data for linkage the pre- 

 ceding experiment was repeated in the winter of 1914, 

 but the linked factors entered differently combined. The 

 experiment was begun by crossing white abnormal fe- 

 males to wild males which gave red abnormal females 

 and white abnormal males. These were inbred and gave 

 the following results in five different cultures (kept with 

 abundance of moist food). 



TABLE II [ 

 Parents: WAb 9 by RX J 

 F,: BAb $ — WAb c? 



The sum of the two non-cross-over males (251 + 312 = 

 563) plus the cross-overs (16) divided into the sum of 

 the cross-over males (7 -f- 9 = 16 ) gives 2.7 as the percent- 

 age of crossing over. Since the white normal males 

 may receive contributions from the changed white ab- 

 normal, the result may be freer from error if the two 

 correlative abnormal male classes, viz., red abnormal (7) 

 and white abnormal (2f)l), be utilized to calculate cross- 

 ing over. Dividing the former by the total (251 + 7) 

 gives 2.7 per cent, of crossing over which is the same as 

 the preceding estimate. 



The reciprocal cross, RN $ by WAb d\ was also made 

 once and the result- in V. coi 

 results are as follows : 



with 



