Which type of mutation involves the insertion or deletion of a nucleotide, potentially altering the reading frame?

A frameshift mutation occurs when there is an insertion or deletion of one or more nucleotides in a DNA sequence. This alteration can shift the reading frame of the genetic code, which subsequently changes how the triplets of nucleotides are grouped into codons. As a result, all amino acids downstream of the mutation may be altered, potentially leading to significant changes in the resulting protein's structure and function. This can have dramatic biological effects, as the altered protein may no longer be functional or could have new functions.

In contrast, substitution mutations involve replacing one nucleotide with another, which typically does not shift the reading frame; nonsense mutations introduce a premature stop codon, which results from a specific type of substitution; and deletion refers specifically to the removal of nucleotides but does not always imply a frameshift unless the number of nucleotides deleted is not a multiple of three. Therefore, the characteristic nature of a frameshift mutation is its potential to disrupt the entire downstream translation of a protein due to changes in the reading frame.