380 



ENERGY LOSS AND BIOLOGICAL EFFECTS 



ated single cells with unpaired recessive defects may be reirradiated. 

 The sites of pairs where unpaired defects occur should be more sensitive 

 to radiation than undamaged pairs of sites. Figure 13 graphically 

 illustrates the presence of weak spots in the damaged cells. The survival 



Diploid yeast with defects 

 r= 1 r = 2 r = 3 



Ar= survivors 

 D = dose 



n = number of compartments 



r = number of defects 



a = constant 



Fig. 13. In the diploid yeast cells which survive, the radiation produces some un- 

 paired defects but no paired ones. The graph shows, in a schematic fashion, different 

 types of diploid cells having unpaired defects. The weak spots in the defective cells 



are indicated by arrows. 



curve of a diploid cell with n essential sites and r unpaired recessive 

 defects can be described by the equation : 



A^ = iVo(2e- 



-aD 



2aD\n — r 



-raD 



(12) 



A family of such survival curves is shown in Fig. 14. Further, if our 

 hypothesis is true, the frequency with which defective cells occur in a 



100 



.^ 80 



60 



40 



20 



Fig. 14. 



20 



40 



60 

 Dose, krep 



80 



100 



120 



Theoretical survival curves for diploid yeast cells with unpaired defects and 

 normal diploid and haploid survival curves. 



