300 CHARLES ZELENY 



Tice further located the gene for bar eye in the sex chromosome, 

 and on the basis of percentage of crossing over with other sex- 

 linked factors it was put at 57 cross-over units from yellow. She 

 considered bar as a dominant to full eye, and it is so described 

 in various papers by Morgan and others. Strictly speaking, the 

 heterozygous condition is intermediate between bar and full. 

 According to the method used here, the heterozygotes between 

 low bar (F 24) and full are +23.89 factorial units from bar and 

 only —7.23 such units from full (table 7). If 100 per cent repre- 

 sents a condition of complete dominance and per cent of com- 

 plete recessiveness, bar has a dominance coefficient of 23.2 per 

 cent and full of 76.8 per cent. If either is to be considered as a 

 dominant, the term should be applied to full eye rather than to 

 bar eye. 



Bar eye has a high degree of stability, though there is an occa- 

 sional mutation such as the reverse mutation to full. Such re- 

 verse mutations are apparently actual returns of the gene to the 

 original condition. The writer has noticed several of them in 

 his stocks and several other germinal changes, among which is 

 the one described in the present paper. 



THE ORIGIN OF ULTRA-BAR 



Ultra-bar also appeared in a single male. This male with but 

 19 facets appeared in the second low selected generation of the 

 white-bar line on October 20, 1917. A cross with a 44-facet 

 sister gave a pure stock in Fa. The ultra-bar thus established 

 has remained stable in character except for the mutations de- 

 scribed on page 304 ff. 



The average facet number is 21.96 in the females and 23.04 

 in the males as opposed to 61.8 and 75.6 in the second low gener- 

 ation of white bar from which it was derived and 810.6 and 849.8 

 in the full eye. In factorial units the second low generation of 

 the white-bar line is —25.93 and —24.59 units from full. Ultra- 

 bar is —10.53 and —11.52 units from the second low generation 

 of white bar and —36.46 and —36.11 units from full eye. Typ- 

 ical representatives of full eye, bar, and ultra-bar are shown in 

 figure 1. Table 1 gives the values of the means, the ranges, and 



