Genetics: Analysis and Principles 5th Edition by Robert Brooker

Exercise 26

As shown in Figure 7.16, phages with rII mutations cannot produce plaques in E. coli K12( ), but wild-type phages can. From an experimental point of view, explain why this observation is so significant.Figure 7.16 A comparison of noncomplementation and complementation. Four different T4 phage strains (designated 1 through 4) carry rII mutations in gene A or gene B. (a) If the rII mutations are in different genes, a coinfected cell can produce new phages and plaques will form. This result is called complementation because the defective genes in each rII strain are complemented by the corresponding wild-type genes. (b) If E. coli K12( ) is coinfected with two rII phage strains with mutations in the same gene, noncomplementation will occur.