64 MUTATIONS 



Novick: May I ask a question? Let's imagine, as a result of heating 

 your bacteria, you produce bacteria that have become metabolically 

 abnormal for a while after growth begins. The longer you heat the 

 bacteria, the higher the temperature, the larger the fraction of the 

 population that becomes metabolically abnormal. Let's say that as 

 a result of being metabolically abnormal, mutation is more probable. 

 The mutation actually occurs during growth, in the relatively small 

 fraction of the population which is metabolically abnormal. Now, the 

 longer you heat, the more mutations you apparently will produce, as 

 you said. 



Now, when did the mutation occur? When you heated it or when 

 you grew it? 



Zamenhof: Suppose I extract DNA after heating, without letting 

 the dry cells divide, and prove that the change is already there. If 

 upon the introduction of this DNA to normal bacteria, I could trans- 

 form them to a mutant? 



Atwood: Then we would have a fact. 



Auerbach: I quite agree. Where you can analyze the process in such 

 a way that we find out which part of the whole process produces this 

 change in base seciuence, then we can say where the mutation occurs. 

 But we usually can't at this stage. It's a question of terminology at 

 the moment. 



Benzer: There seems to be some disagreement as to what the title 

 of the symposium refers to, namely the word, "mutation." Could the 

 Chairman tell us what it is? 



Atwood: May I answer that? 



Neel: Dr. Atwood is undertaking to answer your question. 



Atwood: I suggested in a private discussion a few minutes ago that 

 one ought to use only operational terms, but since some operational 

 terms for mutation are going to be different, depending on the user, we 

 would like to know what are your operational terms? What does a 

 mutation mean in your system? 



Benzer: To me, something to be called a mutation has to involve a 

 change and this change has to be demonstrated to be heritable. 



Atwood: And that is all? 



Benzer: There are all kinds of subclassifications after that, but, 

 to me, these two criteria are necessary. Without them one cannot 

 use the word. 



Neel: You said it has to involve a change. A change in what? 



Benzer: A change in characteristics. 



Stern: Would you call the origin of petites in yeast a mutation? 



