INFLUENCE OF PLOIDY IN YEAST 



245 



1.0 

 09 

 0.8 



0.7 

 0.6 



0.5 

 0.4 



0.3 



0.2 



200 



Dose, ultraviolet rays, ergs x mm " 

 400 600 800 1000 1200 



1400 



0,1 



100 200 



Dose, x-rays, kr 



300 



Fig. 2. Survival curves at 5 min in the case of multiple infection system, with ultra- 

 violet and x-rays. [Latarjet (15).] 



INFLUENCE OF PLOIDY IN YEAST 



We have just observed the influence of multiplicity of units on sensi- 

 tivity, taking as a criterion injury of cytoplasmic elements. Let us 

 now consider the influence of a nuclear constituent, comparing haploid 

 and diploid cells of the same species of yeast as to inhibition of their 

 division by x-rays. 



All the survival curves obtained for yeasts are sigmoid in shape. 

 Especially with x-rays, the most precise determinations give two-hit 

 curves. Using ionizing radiations with increasing ionization density: 

 x-rays of 0.7, 4.15, and 8 A, and alpha rays of polonium, it has been 

 shown (7) that two distinct units are affected, as all these radiations 



