126 



CELL HEREDITY 



Production of 

 transducing phages 



nfection of 

 str-r bacterium 



Disintegration of bacterial 

 DNA and multiplication of 

 vegetative phages 



Formation of mature phages 

 incorporating fragments of 

 bacterial DNA 



Transduction 



Lysis of donor bacterium 



One daughter bacterium has DNA 



formed by copying str-r locus 



from transducing fragment 



Infection of str-s 

 recipient bacterium 



Replication of DNA 



FIGURE 5.7. A diagram of the transduction process showing some of the steps that 

 may be involved. 



chance of becoming incorporated in the host s genotype. In Figure 5.7 

 the host DNA is shown as a fragment separately picked up by the phage 

 coat; as we shall see, at least in some cases, part of the DNA of the trans- 

 ducing phage has been replaced by host DNA through a process of re- 

 combination. 



In the case of lysogenic conversion, the genotype of the bacterial 

 donor of the phage makes no difference; the genotype of the prophage 

 alone determines conversion. On the other hand, in transduction, the 

 donor's genotype is critical. For example, phages grown on a trypto- 



