If the wild type DNA reads "THE CAT ATE THE BIG RAT," what would be the mutation that changes it to "THE CAT ATE THE BAG RAT"?

The correct choice is a substitution mutation because it involves the replacement of one nucleotide with another. In the example provided, the word “BIG” is replaced with “BAG.” This indicates that a single letter in the DNA sequence (the letter "I" in "BIG") has been substituted by another letter (the letter "A" in "BAG").

Substitution mutations are significant in genetics because they can lead to changes in the amino acid sequence of proteins, depending on where they occur and their nature (whether they are silent, missense, or nonsense). In this particular case, the mutation is a perfect example of where a single base change results in a change in a specific word while the overall length and structure of the sentence remain intact.

Other types of mutations described in the options do not fit this scenario. Deletion mutations refer to the loss of one or more nucleotides, insertion mutations involve the addition of nucleotides, and frame shift mutations result from insertions or deletions that alter the reading frame of the genetic code. None of these mutations accurately represent the change from "BIG" to "BAG," making substitution mutation the appropriate term for this specific alteration.