PROBLEMS OF MEASUREMENT OF MUTATION RATES 39 



Atwood: Yes, Dolichos anti-Ai. You mean, to know if it was an 

 A2B? 



Cotterman: Yes; if there is some difficulty in subtyping, you know, 

 with certain reagents. I haven't studied an 11-month-old infant, but 

 on anti-Ai, while Dolichos is an excellent reagent for an adult, it does 

 not work well at all on newborns. 



Auerbach: Are these estimated rates high enough that if you retested 

 a person in, say, five years, you should find a difference, even on the 

 lower estimate of mutation frequency? 



Atwood: In ten years you could. The first experiments were 

 done about three and a half years ago. But I think that the few 

 family studies we now have strongly suggest that there is not going 

 to be much effect of age. 



Lederherg: You mean, there is a strong age dependence, but your 

 technique is completely unable to show it because of the scatter of 

 individuals? 



Atwood: No, I surmise it does not show because such a large propor- 

 tion of exceptional cells is already present in infancy. 



Figure 11 shows a family in which both parents are AB, one is AiB, 

 and one is some subgroup of A. I don't want to call it A2 necessarily, 

 because of the following: when we took the parent who was originally 

 grouped as A2B, and two children, one aged 4 and one aged 22 months, 

 and did the isotope-dilution experiment, we got the results shown in 

 this inset. Each of them has about 30 per cent of inagglutinables as 

 might have been expected from the appearance of the slide test. This 

 is the kind of mosaic that you have worked on, Dr. Cotterman. 



Cotterman: Yes. Did you say that one parent was AoB and the 

 child seemed to be something that you might want to call even 

 weaker than an AoB? 



Atwood: No, in this instance they are alike; perhaps they should 

 be called A3B. The mosaicism of this particular phenotype is already 

 manifest in the young child. This is the parent who was an AiB ; she 

 had 6 X 10"^ non-A cells. These (A3B) individuals had about 30 per 

 cent of non-A cells, and these are two other members of the sibship. 

 One of them is a twin of one up here, a dizygotic twin, of course. 

 Here is the pedigree. This pair of twins is an A1A3 and A3B, and 

 they are four years old. This other A3B is about two years old, and 

 this AiAs is five years old. 



These are two AiAs's and they have levels which are just about the 

 right amount less than that of the AiB parent so that it would be safe 

 to say that the mosaicism associated with this subgroup is quite 

 independent of the loss of Ai. In other words, the subpopulations that 



