Chromosomes and Genes 139 



the so-called exaggeration phenomenon discovered by Mohr (1923a). 

 With these facts in mind we may study the following enumera- 

 tion of the phenotypes of diflFerent compounds, in which — stands 

 for deficiency, R( + ) for a rearrangement near the normal ci locus, 

 and R(ci) for a rearrangement near the mutant ci locus. Only hap- 

 loid and diploid combinations are registered, and our interest is 

 centered upon the position effect (Dubinin effect), not the problem 

 of genie action as such. 



normal at 25° 



slightly ci at 18° 



at 14° more abnormal than +"'/" 



slightly ci 



normal at 25°, slightly ci at 14° 



ci effect 



more extreme ci effect 



normal (at 25°) 

 normal 



normal, but R(2)+/R(2)-|- is like ci/ci 

 ci effect, sometimes intermediate between ci/ci and -}-, 

 sometimes more extreme than ci/ci in different rearrange- 

 ments 



little ci effect, varies for different R, but more deficient 

 sometimes than ci/4- 



more extreme ci than ci/ci and R(ci)/— and ci/ — 

 normal or almost normal 

 extreme type from 9/ — , less effect than ci/ci 

 with least ci effect in no. 10/R(-|-), extreme ci type 

 some similar to ci/ci, some more normal 



A comparison of no. 1 with no. 6, and no. 4 with no. 9 shows 

 what we. may call the typical position effect, not different from other 

 position effects. No. 10 or nos. 1 and 2 show that the variabihty of 

 the ci effect around a threshold, both in different temperatures and 

 with different alleles, applies also to the position effect. However, 

 there is a great difference when a deficiency is involved. No. 5 shows 

 the typical exaggeration, whereas the corresponding no. 7 is normal, 

 meaning that here the position effect has failed to act. But when 

 the position effect is put with homozygous ci (no. 11), it adds its 

 action and a more extreme action results. The normality of the 

 homozygous rearrangement no. 8 is the greatest difference from a 

 standard position effect. The combination no. 13 is working in the 

 same direction and does not show the exaggeration effect; actually it 



