406 



PHYSIOLOGY OF THE FUNGI 



strain of the opposite sex to determine if the changes were inherited. The 

 ascospores from these crosses were planted on both the minimal medium 

 and a complete medium. The appearance of the deficiency in half of 

 the cultures was considered as evidence that the change was of genetic 

 origin; i.e., a mutation. Transfers of the mutant to four different media 

 (minimal, with amino acids, with vitamins, and complete) then deter- 

 mined whether the deficiency was for an amino acid or a vitamin. All 

 media contained biotin. For a diagrammatic scheme of the procedure 

 see Fig. 79. 



X-ravs or 

 ultraviolet 







-^ © © © - 



Coniolict 

 (asexuoil spores) 



Wild fv/pe 



O 



J- 



^ 



\.y 



Crossed 

 with wild 

 t^pe of 

 opposite 

 sex 



Frui+inq body 



I 



-<r- 



V. 



Sexut^l spore 



Complete 



meolium 



(with vitoimins, 



oimino cicids, 



etc.) 



T 



O 



T 



T" 



n 



A 



\y 



Minim(7il Complete 



MinirriCTl Vitoimins Amino 



medium acids 



Fig. 79. Experimental procedure by which biochemical mutants are produced and 



detected in Neurospora. (Courtesy of Beadle, Am. Scientist 34 : 37, 1946, and Science 



in Prug'-ess, 1947. Published by permission of the Society of the Sigma Xi.) 



7 he identification of the specific deficiency involved the growth of the 

 iiiyt2,nt upon the minimal medium plus each of the amino acids and 

 vitamins added singly. This procedure is shown in Fig. 80. Figure 81 

 shows the proof of inheritance of the deficiency for pantothenic acid. 



Mutations involving tli'^ following vitamins have been described: 

 thiamine, riboflavin, pyridoxin'^, niacin, pantothenic acid, p-amino- 

 ben.^oic acid, inositol, and choline. All mutants, as well as the wild 

 type, are deficient for biotin. In addition, mutations have appeared 

 which cannot synthesize tlis following amino acids: arginine, isoleucine, 



