Chapter 8, Problem 4P

An example of a portion of the T4 rIIB gene in which Crick and Brenner had recombined one + and one − mutation is shown here. (The RNA-like strand of the DNA is shown.)

wild type 5′ AAA AGT CCA TCA CTT AAT GCC 3′

mutant 5′ AAA GTC CAT CAC TTA ATG GCC 3′

a.	Where are the + and − mutations in the mutant DNA?
b.	The double mutant produces wild-type plaques. What alterations in amino acids occurred in this double mutant?
c.	How can you explain the fact that amino acids are different in the double mutant than in the wild-type sequence, yet the phage has a wild-type phenotype?