What term describes a change in the base sequence of a gene caused by the substitution of a single base with a different base?

• A. Insertion mutation
• B. Deletion mutation
• C. Chromosomal mutation
• D. Point mutation

Answer: (D)

A single-base substitution in the DNA sequence of a gene is called a point mutation. This change affects only one nucleotide and does not involve adding or removing bases. Insertion mutations add nucleotides, deletion mutations remove them, and chromosomal mutations involve larger-scale changes to chromosome structure. The defining feature here is the one-base change, which is what characterizes a point mutation. Depending on the codon, a point mutation can alter an amino acid, introduce a stop signal, or be silent due to genetic code redundancy.