What is the definition of a frameshift mutation?

A frameshift mutation is defined as the insertion or deletion of nucleotide bases in numbers that are not multiples of three. This is critical because the genetic code is read in sets of three nucleotides, known as codons, each of which corresponds to a specific amino acid. When nucleotides are added or removed in quantities that are not multiples of three, the reading frame of the sequence is altered. This means that all the codons downstream of the mutation will be misread, potentially resulting in a completely different sequence of amino acids, which can lead to significant functional changes in the resulting protein or make it nonfunctional. This explains why option B correctly defines a frameshift mutation.

In contrast, a substitution of a single nucleotide base refers to a point mutation, which can affect only one amino acid without changing the entire reading frame. A change in a single amino acid is a consequence of a point mutation, not a frameshift. Lastly, copy number variation involves large duplications or deletions of DNA segments rather than the shifting of the reading frame due to the insertion or deletion of single or multiple nucleotides that are not in multiples of three.