Answer:
The type of chemical mutagen to choose depends on the intended effect. In this case, the best ones are acridines and nitrous acid.
Explanation:
Brenner et al. proposed that acridines induce mutations by causing deletions or additions of single base pairs during replication. Acridines bind to DNA by intercalation between adjacent base pairs. Acridines inactivate extracellular phage by photodynamic action but the necessary conditions for this killing
are avoided in the procedure for acridine-induced mutation of reproducing phage. The lack of reported acridine-induced mutation in organisms other than phage raises some questions as to the generality of its
mutagenesis, thus making it a good type of compounds to induce specific mutations.
In the other hand, nitrous acid deaminates the amino bases adenine, cytosine (and hydroxymethylcytosine) , and guanine in nucleic acids.
Analysis of the effect of differences of pH during nitrous acid treatment
of phage DNA showed that the rate of killing was affected similarly to
the rate of guanine deamination, and that the rates of induced r mutation was affected similarly to the rates of adenine and hydroxymethylcytosine deamination. Ascribing the induced mutations to deamination of adenine and cytosine is reasonable in terms of the hydrogen bonding of their products and the Watson-Crick base pairing schemes. Since this inorganic acid is molecule-specific, it would also be used to induce certain mutations in bacteria without causing transition mutations.
