Payne: Variations and Selection 



19 



I have used two methods. The first was to get rid of the 

 X-chromosome by outcrossing and inbreeding to produce a 

 strain with both members of the second, third, and fourth 

 chromosome pairs from the selection hne and the X-chromo- 

 some from some other hne. This was done by crossing the 

 selection line male to a bar-eyed female. The males from 

 this cross get their X-chromosome from the bar line and will 

 get one member of each of the second, third, and fourth 

 chromosome pairs from the selection line and the other 

 member of each of these pairs from the bar line. These 



TABLE IV 



Offspring 





Normal 



Extra 

 Bristles 



Total 



Mean 

 Bristles 

 Number 



Selection line male x bar female 



168 



70 



238 



4.436 



Fi male x bar female from stock 



375 



12 



387 



4.033 



F2 X Fo 



986 



206 



1192 



4.233 



F3 X F3 



454 



252 



706 



4.573 



F4 X F4 



196 



267 



463 



5.066 



F5 X F5 



163 



237 



400 



5.260 



Fe X Fe 



417 



680 



1097 



5.188 



Table IV gives the data from the cross of the selection line male to 

 a bar female. The Fi bar male was mated to a bar female from stock. 

 The flies with bristles were inbred and, in the next three generations, 

 flies showing the highest number of extra bristles were used as parents. 

 The table gives the number of flies in each generation >vhich have the 

 normal bristle number (four), the number of flies with extra bristles, 

 the total number of flies, and the mean bristle number of all the flies. 



F-, bar males (bar is dominant) were mated out to bar females 

 from stock. All the Fo flies thus produced would have 

 X-chromosomes from the bar line. They might get one mem- 

 ber of each of the second, third, and fourth chromosome 

 pairs from the selection line, or they might get only two or 

 one or none at all from this line. If there are factors for 

 extra bristle number in any of the chromosomes other than the 

 first, and if they are dominant to the normal, some of the F. 

 flies should have extra bristles. Twelve of the females did 

 have extra bristles. These were mated to their normal F. 

 brothers. Of the F.. offspring, 986 were normal and 206 had 

 extra bristles (for the number of extra bristles and the mean 



