300 



n 11 



CHROMOSOME 



TRANSFORMING 

 SEGMENT 



figure 22—5. Postulated mechanisms for the incorporation of a segment of genetic 

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



into the DNA of the host, and that probably 

 either strand of the donor DNA could be 

 used this way. 7 Thus, the evidence favors 

 the breakage hypothesis of integration. 

 It is important to note that the portion 



■ See O. H. Siddiqi (1963), and M. S. Fox and 

 M. K. Allen (1964). 



of penetrating donor DNA which is not in- 

 tegrated, obviously, is also not retained or 

 conserved as chromosomal genetic material. 

 If integration occurs by copy-choice, the 

 transforming segment is not conserved 

 either; if integration occurs by "breakage- 

 exchange." the replaced DNA segment is 

 not conserved. 



