In describing a base substitution mutation, which option shows a single nucleotide change?

In describing a base substitution mutation, which option shows a single nucleotide change?

• A. Deletion
• B. Substitution
• C. Insertion
• D. Inversion

Answer: (B)

Base substitution, also called a point mutation, involves replacing one nucleotide with a different one, keeping the DNA length the same. That single base swap is exactly what a base substitution describes. The other mutation types change either the number of nucleotides or the arrangement of a DNA segment: deletion removes bases, insertion adds bases, and inversion flips the orientation of a segment. Because they involve adding, removing, or reordering bases rather than just replacing one nucleotide, they are not single-nucleotide changes. For example, changing a codon from GCA to GTA is a substitution—a single base is changed.

Base substitution, also called a point mutation, involves replacing one nucleotide with a different one, keeping the DNA length the same. That single base swap is exactly what a base substitution describes. The other mutation types change either the number of nucleotides or the arrangement of a DNA segment: deletion removes bases, insertion adds bases, and inversion flips the orientation of a segment. Because they involve adding, removing, or reordering bases rather than just replacing one nucleotide, they are not single-nucleotide changes. For example, changing a codon from GCA to GTA is a substitution—a single base is changed.