Which mutation is defined as a single-nucleotide change in the DNA sequence?

• A. Nonsense mutations
• B. Inversion mutations
• C. Point mutations
• D. Frameshift mutations

Answer: (C)

A single-nucleotide change in the DNA sequence is called a point mutation. This broad category covers substitutions where one base is replaced by another, and it can affect a codon to change the amino acid (missense), create a premature stop (nonsense), or even leave the amino acid the same (silent) depending on the codon context. Inversion mutates a segment by flipping its orientation, which is not just a single base change. Frameshift mutations come from inserting or deleting nucleotides, shifting the reading frame and altering all downstream codons. So the concept described by a single-base substitution is point mutations; a specific subtype like nonsense is just one example of what a point mutation can do.