What happens during an insertion mutation?

An insertion mutation occurs when one or more nucleotide bases are added into the DNA sequence of a gene. This addition can alter the reading frame of the gene, potentially changing how the gene is translated into protein. When a nucleotide is inserted, it can disrupt the normal codon sequence, which may lead to the synthesis of a protein that is drastically different from the intended sequence. This can result in a nonfunctional protein or even a protein with entirely different characteristics.

The other options describe different types of mutations or consequences that do not specifically reflect what occurs during an insertion mutation. For instance, removing a letter refers to a deletion mutation, while reversing a sequence involves a different type of genetic rearrangement. While incorrect protein synthesis can occur as a result of an insertion mutation, it does not directly describe the mutation itself. Therefore, the defining action of an insertion mutation is clearly represented by the inclusion of an extra letter in the sequence.