Chapter 7, Problem 34P

Nine rII^- mutants of bacteriophage T4 were used in pairwise infections of E. coli K(λ) hosts. Six of the mutations in these phages are point mutations; the other three are deletions. The ability of the doubly infected cells to produce progeny phages in large numbers is scored in the following chart.

 

The same nine mutants were then used in pairwise infections of E. coli B hosts. The production of progeny phages that can subsequently lyse E. coli K(λ) hosts is now scored. In the table, 0 means the progeny do not produce any plaques on E. coli K(λ) cells; − means that only a very few progeny phages produce plaques; and + means that many progeny produce plaques (more than 10 times as many as in the − cases).

 

a.	Which of the mutants are the three deletions? What criteria did you use to reach your conclusion?
b.	If you know that mutation 9 is in the rIIB gene, draw the best genetic map possible to explain the data, including the positions of all point mutations and the extent of the three deletions.
c.	One uncertainty should remain in your answer to part (b). How could you resolve this uncertainty?