What does a frameshift mutation result from?

A frameshift mutation occurs when the reading frame of the genetic code is altered, which directly results from the insertion or deletion of nucleotides within a DNA sequence. This type of mutation shifts the entire downstream sequence, meaning that all subsequent codons are misread during translation. For example, if a single nucleotide is added or removed, the ribosome will read the mRNA differently from that point forward, often leading to completely different and typically nonfunctional protein products.

In contrast, substitutions of nucleotides, as mentioned in one of the options, change just one nucleotide to another without altering the overall reading frame, and are classified as point mutations. Point mutations can lead to silent mutations, missense mutations, or nonsense mutations, but they do not cause frameshifts.

Replication errors can lead to various types of mutations, but they are not specifically responsible for frameshifts unless they result in insertions or deletions. Therefore, while replication errors may indirectly contribute to frameshift mutations, they are not the mechanism that defines them.

Thus, the focus on insertions or deletions in the correct answer highlights the critical role these alterations play in creating frameshift mutations, making it the accurate choice in this context.