ROUGHOID. 



37 



May 24, 1919. 



ru + D H 



+ se + + 



X 



ru se + + 



ru se + + 



Summing up the data in the previous tables: 



The value for dichaete hairless (21.6) is approximately the 

 expected result (24.8). Sepia dichaete crossing over is noticeably 

 high, since the average normal value is 11.7 units. This is 

 possibly due to a complicating factor, linked to the new factor, 

 roughoid, and "stretching out" that part of the third chromo- 

 some. More work will have to be done before this can be 

 certain. It will be noticed that the double cross-over class (i, 2) 

 is lower than the triple cross-over class (i, 2, 3). This is un- 

 expected and remains unexplained at the present time. 



SUMMARY. 



(a) A new mutation has occurred in the third chromosome of 

 Drosophila melanogaster to the left of sepia, which for several 

 years has been the leftmost of the known loci. 



(b) There was a roughoid sepia cross-over value of 24.9, based 

 on a total of 2,748 flies of which 685 were cross-overs. 



(c) Associated with roughoid, there is possibly a linkage mod- 

 ifier increasing the crossing over between sepia and dichaete, and 

 perhaps between roughoid and sepia as well. 



