PROBLEMS OF MEASUREMENT OF MUTATION RATES 37 



10-1 O o 



8- 



< 



ID 6- 

 O 



X 



tr 

 c 4- 



cn 



lij 

 o 



2- 



0- 



1.2X10 PER HOUR 



I 1 \ I 1 1 1 



20 40 60 



AGE .YEARS 



Figure 9. Proportions of Phaseolus-negative (solid points) and 

 Dolichos-negative (open points) cells vs. age in A and AB persons. 

 Lines show required rates of origination of exceptional stem lines 

 on the assumption of linear increase from age zero. Subsequent data 

 (Figs. 10-12) show this assumption to be erroneous. 



The black points on Figure 9 are the total non-A and the open 

 circles are the non-Ai— the non-Ai includes phenotypically A2 and 

 cells, summed. The slopes represent the rates of mutation necessary to 

 produce these observed frequencies on the assumption of linear in- 

 crease with age. 



To produce the lowest frequency would have required about 

 1.6 X 10"^ mutations per cell per hour; the highest (for non-A) about 

 10"^ per cell per hour. These open points are too high to be considered 

 as mutant frequencies. 



As you will see, I think the assumption of linear increase from the 

 origin is false. The rates estimated on this false assumption would not 

 be unusual by microbial standards, but are about a factor of 10 above 

 the usual range of human germinal rates. 



These scattered points do not suggest an age effect, but it is not 

 ruled out. The different individuals may have had different rates of ac- 

 cumulation of mutant stem lines. Even if this were true, very young 



