Question

Materials that are suspected to be chemical mutagens are commonly tested by exposing bacterial cultures to high concentrations of the mutagenic agent. The objective of this research is understanding how the chemical causes mutations in the bacterial DNA. A typical procedure includes the following steps:

expose bacterial culture to the chemical agent
isolate bacteria with various mutations in a particular gene
sequence the DNA from the various mutations in that gene
A scientist that is studying a chemical mutagen, claims that nearly all of the genetic mutations caused by exposure to the chemical are either insertions or deletions.

Which argument BEST supports this claim?

A.
The resulting mutation is a base analog that looks like one nucleotide base but base-pairs like another, causing nonsense mutations.

B.
The resulting mutation chemically modifies one nucleotide base to make it incorrectly base-pair, causing point mutations.

C.
The resulting mutation binds together thymine found next to each other in a DNA strand, causing silent mutations.

D.
The resulting mutation appears between existing base-pairs in a DNA double helix, causing frameshift mutations.

Answer 1

D. The claim is best supported if the mutagen inserts extra nucleotides "between" existing base pairs, which produces insertions (or if it removes bases, deletions) and thus causes frameshift mutations that alter the reading frame of the gene.