Biochemical Genetics {II) 



283 



TETRAD 



FIRST 



MEIOTIC 



DIVISION 



8 Spores + 

 + 

 + 

 + 

 th 

 th 

 th 

 th 



FIGURE 32-1. Arrangement of spores in t/ie Neurospora ascus when segregation 



occurs at the first meiotic division {left) and at the second meiotic division {right), 



as determined by the absence and presence, respectively, of a chiasma between the 



segregating genes and the centromere. 



ized this way, they were all found to be on 

 the same chromosome and appeared to be 

 the same distance from the centromere. This 

 suggests that the specificity of a particular 

 enzyme is the result of the action of a particu- 

 lar cistron. 



For the efficient detection of biochemical 

 mutants in Neurospora, certain modifications 

 are made in the procedure already outlined. 

 Potentially mutant spores are grown on a 

 medium supplemented with all substances 

 which might conceivably be involved in bio- 



