302 



Scientific Proceedings (116). 



red-eye were x-rayed soon after emerging from the pupa with a 

 dose just under the sterilization dose and mated to white-eyed 

 males. The white-eyed character being recessive to the red- 

 eyed the normal result of crossing a homezygous red-eyed female 

 with a white-eyed male is for the offspring in the first generation 

 to be all red-eyed if there is no non-disjunction. 



In all, four experiments have been completed to date. In 

 three of these thirty-five virgin females, homozygous for the red- 

 eyed character, were mated with white-eyed males. Nineteen 

 of these were used as controls and sixteen were x-rayed soon after 

 emerging from the pupa and immediately before mating. The 

 rayed females were the sisters of the controls. None of the nineteen 

 control pairs produced white-eyed males. One of the rayed females 

 was sterile. Of the fifteen fertile, rayed females, twelve produced one 

 or more white-eyed males. 



In two of the four experiments the white-eyed males which 

 were crossed with the rayed females were also homozygous for 

 dumpy, a second chromosome character. All of the six excep- 

 tional males produced had normal wings with the exception of 

 one which died before its wings expanded. It therefore seems 

 probable that only the x-chromosome was affected. 



Further experiments using multiple sex-linked stock, eosin 

 miniature and scute-echinus-cut- vermilion-garnet-forked, have 

 shown that probably the whole x-chromosome is affected. 



Since the eggs which produced the exceptional males were 

 laid during the first six days after raying it seems reasonable to 

 believe that they were acted upon while in or preparing for one 

 of the maturation divisions. Further, since the x-chromosome 

 behaves differently from the other chromosomes during these 

 divisions the production of the exceptional males would be ac- 

 counted for if it is assumed that the x-rays were applied to the 

 egg cells from which they came at a time when the x-chromosome 

 in them was in a condition particularly susceptible to the dose of 

 x-rays given. 



