20 



Indiana University Studies 



bristle number in each generation see Table IV) . The extra 

 bristled flies were mated and the line was thus continued for 

 six generations to see whether the mean bristle number could 

 be raised to what it was in the selection line. If so, there 

 certainly could be no factor for extra bristles in the X-chromo- 

 some. If not, it would at least be indicative, if not conclusive 



TABLE V 



Selection line male x eosin miniature female 



Normal Flies, Wild Type 



Eosin Miniature 

 Males 



Normal 

 Bristles 



5 



Bristles 



6 



Bristles 



7 



Bristles 



8 



Bristles 



9 



Bristles 



Normal 

 Bristles 



5 



Bristles 



13 



18 



37 



27 



1 



1 



46 



17 



Fi female x eosin miniature male from stock 





Nor- 

 mal 



5 Br. 



6 Br. 



7 Br. 



8 Br. 



9 Br. 



Total 



Mean 



Eosin miniature 



249 

 190 

 120 

 139 



60 

 55 

 83 

 113 



18 

 21 

 51 

 75 



3 

 4 

 9 

 44 



1 

 1 

 7 

 16 





331 

 271 

 270 

 391 



4.329 

 4.416 

 4.888 

 5.222 



Eosin 





Miniature 





Normal, wild type 



4 



In Table V the selection line was crossed to eosin miniature, and the 

 Fi females were back-crossed to eosin miniature males. The table gives 

 the Fi and the F2 data. Four types of flies appear in F2 as crossing-over 

 occurs in the Fi female. Eosin miniature and normal (wild type) are 

 non-cross-overs, and eosin and miniature are cross-overs. Of the non- 

 cross-overs, eosin miniature has a low mean bristle number (4.329), 

 while the mean bristle number of the normal is 5.222. Of the cross-over 

 type, eosin, the mean (4.416) approaches that of eosin miniature, while 

 the mean of miniature (4.888) approaches that of the normal. 



proof, that there was such a factor in the X-chromosome. As 

 can be seen in Table IV, the mean in the fourth, fifth, and 

 sixth generations was practically the same. The highest 

 point was reached in the fifth generation when the mean was 

 5.26. This experiment then proves conclusively that there 

 is one or more factors outside the X-chromosome and makes 

 probable the presence of a factor in the X-chromosome which 

 influences bristle number. A second test was made by cross- 



