GENETICS OF SOMATIC CELLS 467 



breeding wild mice and take not the best but the worst animals that come out and take 

 a look at them from the point of view, not of their ease of cultivation, but whether they 

 do have noteworthy metabolic defects. 



Dr. Owen: It seems to me that Dr. Klein's system should be well adapted for 

 mapping the H-2 complex. In this connection, as I remember Dr. Sally Allen's early 

 work, 12 the only study I know in which there was a genetic marker external to the H-2 

 complex, there were two instances of apparent recombination, which would have 

 required that the DK components be ordered differently with reference to that marker. 

 Dr. Snell, would you comment on this point ? 



Dr. Snell: One case was thoroughly substantiated. In the other the mouse 

 died before the breeding tests were complete. If that case were a valid recombinant, 

 then the D and K components cannot be arranged in a linear order. However, since 

 the tests were not completed, I do not think much weight can be attached to it. 



Dr. Barrett: In relation to the markers that go along with this, I have ap- 

 proached this subject, of course, from a different viewpoint than Drs. Snell, Hoecker, 

 Gorer, and so on; and I have not used these antigenic components, but I take the 

 transplantability of the tumor, or its nontransplantability, to be a quite adequate 

 indication of its antigenic composition. As a matter of fact, I have been surprised in 

 this discussion of methodology that, although we talked about methods involving very 

 small parts of the animal (sometimes just the molecule), we have said very little about 

 how to use the whole animal in these methods. 



Now I do not want to give my own paper here, but in published work 54 involving 

 very extensive observations of what Dr. Klein has called the Barrett-Deringer pheno- 

 menon, one can see that this phenomenon can be expressed by over-all changes in 

 percentage, usually upward; but let us remember that the upward change is probably 

 only the easier change to find. The cell that has become incompatible automatically 

 commits biological suicide and is hard to find. The other aspect is that if one examines 

 the over-all increases in ratio, one finds that when they are tested in a backcross population 

 in which there are three markers and therefore eight segregants, the change in 

 percentage among these segregants may occur not at all, it may go up a little, it may go 

 up a lot, or it may produce tumors that grow temporarily and regress. All these 

 characteristics can be definitely related to external markers of these animals but cannot 

 be related to agglutination, and apparently have nothing to do with H-2, although I 

 agree with you, Dr. Klein, it appears that H-2 is a stubborn locus in this regard. 

 Compatibility can be related to brown, black, to agouti, and perhaps to albinism. It 

 cannot be related to color on a statistically significant basis, but these markers are there 

 and the change can be related to these external markers. 



Dr. Klein: I should like to add a few words concerning suitable markers. The 

 first question regards the nature of the approach. One may simply want to study 

 somatic-cell variation, one may want to explore the possibility of somatic crossing over, 

 or else one may prefer to engage in attempts to achieve transfer of genetic material 

 between somatic cells. 



