Chapter 8, Problem 5P

Consider Crick and Brenner’s experiments in Fig. 8.4 (p. 259), which showed that the genetic code is based on nucleotide triplets.

a.	Crick and Brenner obtained FC7, an intragenic suppressor of FC0, that was a mutation in a second site in the rIIB gene near the FC0 mutation. Describe a different kind of mutation in the rIIB gene these researchers might have recovered by treating the FC0 mutant with proflavin and looking for restored rIIB+ function.
b.	How could Crick and Brenner tell the difference between the occurrence described in part (a) and an intragenic suppressor like FC7?
c.	When FC7 was separated from FC0 by recombination, the result was two rIIB- mutant phages: One was FC7 and the other was FC0. How could they discriminate between the rIIB- recombinants that were FC7 and those that were FC0?
d.	Explain how Crick and Brenner could obtain different deletion (−) or addition (+) mutations so as to make the various combinations such as ++, − −, +++, and − − − shown in Fig. 8.4c.