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CHAPTER 37 



SEGMENT 



r 



CHROMOSOME 



INTEGRATION COMPLETED 



REPLICATION DAUGHTER 



CHROMOSOME 



FIGURE 37-1. Postulated mechanisms for the incorporation of a segment of 

 genetic information into a host chromosome. A. Breakage method; B. Copy- 

 choice method. 



isms, this may occur under special circum- 

 stances, and may be possible between the 

 visibly less well-defined chromosome of bac- 

 teria and the shorter synapsed segment of 

 transformer DNA. 



The second method might involve what has 

 been called copy-choice (Figure 37-1 B). In 

 this procedure, a daughter chromosome is 

 formed by the alternate use of the normal 

 chromosome and the transformer DNA as a 

 template, so that when completed it is exactly 



like the original chromosome except for a 

 segment that was replicated using transformer 

 DNA as a template. Although we cannot 

 decide by which of these two mechanisms 

 (or yet another) integration occurs, there is 

 evidence that the process is fixed, so that it 

 does or does not occur, within a single gen- 

 eration, and it is likely that the transformed 

 marker is replicated beginning with the second 

 division cycle. 



It is clear that the portion of penetrant 



