Final answer:
Frameshift mutations, such as the deletion of one nucleotide, alter the reading frame of the genetic code and can dramatically impact the protein produced, often leading to a nonfunctional protein.
Step-by-step explanation:
A frameshift mutation is a genetic mutation caused by insertions or deletions of a number of nucleotides in a DNA sequence that is not divisible by three. The result is a shift in the reading frame of the genetic code. Of the options provided, a deletion of one nucleotide (D) would be considered a frameshift mutation. Unlike a deletion of an entire codon (A), which removes a set of three nucleotides and therefore does not disturb the reading frame, the deletion of a single nucleotide changes the entire sequence of codons, often leading to a nonfunctional protein.
As an illustrative example, consider a simple sequence of RNA: AUG-AAU-ACG-GCU. If a single nucleotide is deleted early in the sequence, it would shift the reading frame and potentially alter every subsequent amino acid that is coded for. This could have a dramatic effect on the resulting protein's structure and function. Alternatively, a frameshift could also occur through an insertion, such as adding an extra A nucleotide after the start codon AUG, changing the sequence of amino acids that follow.