No. 576] 



VARIATION IN DROSOPIIILA 



741 



gave no Beaded offspring either in the first generation or 

 in the F 2 generation, although nearly one thousand of his 

 grandchildren were carefully examined. The remaining 

 male was abundantly fertile and had one son exactly like 

 his father in appearance (with a slight nick at the tip of 

 the wings). The rest of his offspring were normal. This 

 son was sterile. 



TABLE XXIX 



FitfXKnk 9 .. 1 I 859 504 I 580 223 



The results of these tests with five of these supposed 

 "cross-over" males show clearly that they were not nor- 

 mal Beaded flies. As said, they might represent muta- 

 tions, or the dominance of the gene 1, or some abnormality. 

 These are mere guesses, but since there are no authentic 

 cases on record in Drosophila of crossing over in the male 

 sex in those cases where the mutants dealt with are well 

 known genetically, i. e., since the only apparent cases 

 occur in the Beaded wings and some of the other not 

 well-known and peculiar mutants of Drosophila, we are 

 not justified in assuming that such crossing over takes 

 place here. 



III. THE EFFECT OF ENVIRONMENTAL CONDITIONS UPON THE 

 PEODUCTION OF BEADED WINGS 



A. General Statement 

 If we have so far interpreted the evidence correctly we 

 may formulate the following statement as a provisional 

 hypothesis. A gene B' located in the third chromosome 

 near that for Ebony is directly responsible for the pro- 

 duction of Beaded wings. By itself in the homozygous 

 condition, the fly bearing it may have normal wings, 

 though it usually will have wings somewhat Beaded. In 

 the heterozygous condition, it is rarely, though sometimes, 



