GENES IN THE MALE OF DROSOPHILA. 



201 



Purple-eyed, long-winged flies were mated to red-eyed, vestigial 

 flies, and gave normal Ft flies. When the FI males were bred 

 to purple vestigial females the following results were obtained : 



Here again the results are explicable on the hypothesis of 

 non-crossing over in the male. The recessives enter the FI 

 male from opposite sides, i. e., they lie in different but homologous 

 chromosomes. Hence if no crossing over occurs in the male each 

 spermatozoon will contain one or the other recessive, and since 

 the eggs are all alike and carry only double recessive factors only 

 two types of zygotes are expected. 



When the FI females, sisters to the males just tested, were 

 likewise bred to purple vestigial males, the following classes 

 result: 



Red Long. 

 265 



Purple Long. 

 2,203 



Red Vestigial. 

 2,038 



Purple Vestigial. 

 234 



Crossing over in the female (about 10 per cent.) explains the 

 classes that appear in this experiment. 



These results with purple vestigial are comparable at every 

 point with those for black vestigial and both furnish evidence 

 of no crossing over in the male. The numbers are large enough 

 to make it highly probable that crossing over in the male did 

 not occur. 



FURTHER EXAMPLES OF NON-CROSSING OVER IN THE MALE 

 BETWEEN GENES IN THE SECOND PAIR OF CHROMOSOMES. 



The following data are taken from experiments that Mr. C. B. 

 Bridges and the author are carrying out. The records have been 

 made by Mr. Bridges. A recessive mutant called "dachs" 

 (from the short legs of the flies) was combined with another 

 character also in the second group, viz., black. When the double 

 recessive dachs black is crossed to the wild (normal gray) fly 



