What type of mutation involves replacing a nucleotide in the DNA sequence with a different nucleotide?

A substitution mutation involves replacing one nucleotide in the DNA sequence with a different nucleotide. This can happen when a single base is altered, which may lead to the incorporation of a different amino acid during protein synthesis or potentially a synonymous change where the same amino acid is maintained due to the redundancy of the genetic code. The key characteristic of a substitution mutation is that it directly affects the nucleotide sequence without altering the overall length of the genetic material, contrasting with other types of mutations.

For example, if the original DNA sequence is ATC and the mutation changes it to ACC, a substitution has occurred. This can have varying effects on the resulting protein, depending on whether the new codon specifies a different amino acid or not. The focus of a substitution mutation specifically on one nucleotide distinguishes it from other mutations like insertion and deletion, which add or remove nucleotides, thereby changing the overall length and potentially shifting the reading frame of the codons.

Frameshift mutations, on the other hand, result from insertions or deletions that shift the entire reading frame of the genetic code, altering all downstream amino acids. Thus, substitution mutations are distinctive in their mechanism of altering a single nucleotide while maintaining the overall integrity of the sequence's length.