20 Discussion 



Rotblat: What are the advantageous effects which one may expect 

 from radiation in heterozygous conditions ? 



Griineberg: It appears that these are improvements of general 

 viability. In Drosophila the chronic irradiation experiments of 

 Bruce Wallace (1957. Proc. not. Acad. Sci. (Wash.), 43, 404) indicate 

 that the exposed population on the whole increased in viability 

 rather than the reverse. The effects on general viability are ap- 

 parently due to hybrid vigour, due to the presence of freshly arisen 

 mutations in heterozygous condition. 



