140 



STURTEVANT 



Table 23 

 Facet numbers of flies carrymg various coj/ibinatiojis of bar allelomorphs 



Since the bar allelomorphs are to be 

 thought of as inhibitors of facet de- 

 velopment, it will be seen that this 

 comparison indicates that two bar al- 

 leloTiiorphs lyhig in the scnne chromo- 

 some are ?Twre effective than are the 

 sa?}ie two allelomorphs when they lie 

 in opposite chromosomes. 



Such an unexpected result must of 

 course be checked up carefully. Only 

 two possibilities of avoiding the above 

 conclusion seem open. The results are 

 due to ( 1 ) accidental differences in 

 temperature or modifiers; or (2) the 

 round allelomorph of bar brings about 

 a reduction in facet number just as 

 does bar. Both of these possibilities can 

 be eliminated, as the following parr.- 

 graphs will show. 



There is no temperature effect, 



since in each case the cultures were 

 reared side by side; and in the case of 



— versus — — , several different tests all 



gave the same type of result. 



If the results are due to accidental 

 modifiers it is scarcely conceivable 

 that these should lie anywhere but near 

 the bar locus, because of the inbreed- 

 ing to which the stocks have been sub- 

 jected. As will be shown below, 

 another bar chromosome (derived by 

 mutation from the inbred BB of this 

 strain) has been found to give results 

 sufficiently close to the bar used here 

 so that the conclusions as to the effect 

 of position must apply also to the new 

 bar. And two other not-bar ("round") 

 chromosomes have been found to give 

 substantially the same result as the one 



