172 Nature of the Genetic Material 



vermilion, according to Green (1954), The details (Lewis, 1952), 

 however, are not as clear as such a general statement may suggest. 

 In Stubble-stubbloid there are two bands not forming a capsule and 

 not completely equal. Still less convincing is the bithorax situation 

 (fig. 12). Here the section in question shows a doublet (89E1-2) 

 and the bithorax locus is assumed to be "in the immediate vicinity 

 of, if not within" this doublet. "The locus of bithoraxoid is most 

 probably in the adjoining 89E3-4 doublet, although the possibility 

 that it lies one or two bands to the right of this structure is not 



58.2- 58.2 5 8.8 58.8* 58.8- 58.9t 

 sbd Sb S5 bx Bxl bxd Mc 



Fig. 12. Section from middle of right arm of third chromosome of D. 

 melanogaster showing location of pseudoalleUc series of bithorax (bx), bitho- 

 raxoid (bxd), and Bithorax dominant (Bxl). (From Lewis, 1951; reproduced by 

 permission of the author.) 



excluded. The two doubles of subdivision 89E are possibly partially 

 homologous to one another, in the sense that they frequently appear 

 as one coalesced structure" (Lewis, 1951). The theory of repeats, 

 it seems to me, should lead us to expect a clear-cut triplet here as 

 the proper location for the "genes." The foregoing description by 

 Lewis seems to fit much better the idea of a chromosomal segment 

 in which whatever happens on a microscopic or submicroscopic level 

 produces an allelic effect. In the present case, Lewis excluded the 

 presence of visible rearrangements. He produced, however, by X-ray- 

 ing, a number of rearrangements with a break left of the region 



