12 MUTATIONS 



on the average, approximately 80 spermatozoa. However, I don't be- 

 lieve this alters the basic argument. There are some additional com- 

 plications; nevertheless, this is still essentially a building-off from one 

 cell that remains. 



Atwood: A process of bifurcation of the lines is possible, because 

 that is what must happen if you kill off some cells and they then re- 

 generate. They must make up the number by dividing the lines them- 

 selves. That can happen. 



Spuhler: Kim, do you have to worry about lines that are killed by 

 the events of mutation? Is it a maximum? 



Atiuood: They would just be replaced, I surmise. You can regard the 

 system as being the same size, approximately, during the time it is 

 functioning. 



Zamenhoj: What is the present status of the finding that, in Dro- 

 sophila, old spermatozoa include more mutations than the young 

 spermatozoa (10) ? 



Dobzhansky: Detailed data, to my knowledge, have never been 

 published. 



Zamenhof: I hope we'll get to a discussion of mutations in stationary 

 cells as compared to where division is going on (32). 



Goldstein: Do we know anything about the average interval in the 

 average germ cell line? 



Atwood: I don't know. The question of what weights to give to the 

 contributions of mutant gametes from these two periods in the ontog- 

 eny of the germ cells is one that we could answer if we knew whether 

 the mutation rate is the same during the one time as it is during 

 the other. If the mutations per division were the same in man, you 

 would get about ten years' worth of mutation or mutant gametes out 

 of the embryonic period. 



Neel: You mean that mutationally speaking, the embryonic period 

 makes the same contribution as ten years of adult life? 



Atwood: Yes; that is, you would have as great a proportion of 

 mutants at the end of the embryonic period as you would add during 

 ten years of later life. 



Novick: I'm sorry to interrupt, but I can only understand this if 

 what Dr. Goldstein says is correct; that is, if the growth rate is differ- 

 ent, the generation time is different or the interval is different. 



Atwood: The generation time is very different. 



Goldstein: What generation time do you assume when you give 

 that figure of ten years? 



Atwood: Well, I derived this from the generation time in bone 



