166 



"rounding-up" tendency of the synap- 

 tic attraction alojig the chromosome in 

 addition to the oblique attractions and 

 the straight-across attractions. 



The Bar-eye reduction is thus seen 

 to be interpretable as the effect of in- 

 creasing the action of certain genes by 

 doubling or triplicating their number— 

 a genie balance effect. But "position 

 effects" are never excluded when du- 

 plications or other rearrangements are 

 present, either in the wedging further 

 apart of genes normally closer, or by 

 the interaction with new neighbors. 

 The respective shares attributable in 

 the total effect to the genic-balance 

 change and to the position-effect 

 change seems to be at present a matter 

 of taste. 



BEADLE AND TATUM 



Study of the Baroid translocation 

 apparently shows that the break in X 

 comes between the two halves of the 

 heavy doublet of 16A1. The break in 

 2R follows directly after the heavy 

 capsular doublet of 48C1. Thus a de- 

 monstrable basis is laid to Dobzhan- 

 sky's interpretation of the Baroid eye- 

 reduction as a position effect.^ 



The previously reported finding * of 

 the presence of "repeats" as a normal 

 part of the chromosomes of D. me- 

 lauogaster, and the suggestion that un- 

 equal crossing-over is probably the 

 mechanism of production of some 

 short repeats, thus have received ample 

 verification bv^ these direct observa- 

 tions on these processes in the case of 

 Bar and its derivatives. 



Genetic Control of Biochemical Reactions 

 in Neurospora 



G. W. BEADLE and E. L. TATUM 



Reprinted by authors' and publisher's permis- 

 sion from Proceedi?7gs of the National Academy 

 of Sciences, vol. 27, 1941, pp. 499-506. 



In my remarks on Sewall Wright''s paper (page 18) I pointed out 

 that the approach implicit in that work was one of the most promis- 

 ing aspects of genetic research. The problems facing Wright ajid his 

 students were enormous, however, and ?nost of them ste?fm?ed fro7n 

 the difficidties of working with the mouse. It is practically impossible 

 to tamper with the mouse'' s enviro7iment experimentally , ajid it is 

 ah/jost as bad to try to achieve uniformity of genotype in a large 

 sample. The problevn of the biochemistry arid physiology of the 

 gene required a new orga?iis77t for successfid ijivestigation, although 

 Wright's methods were still proving fruitful. 



