Which type of mutation involves the replacement of one base with another?

Substitution is a type of mutation where one base in the DNA sequence is replaced with another base. This change can occur without altering the overall length of the DNA molecule and can potentially lead to changes in the amino acid sequence of a protein. Depending on which base is substituted, this mutation might be silent (having no effect on the amino acid sequence), missense (resulting in a different amino acid), or nonsense (creating a premature stop codon).

In contrast, the other types of mutations involve different mechanisms. Insertion mutations add one or more bases to the DNA sequence, while deletion mutations remove one or more bases. Both of these alterations can disrupt the reading frame of the gene, leading to more extensive changes in the resulting protein. Frameshift mutations, in particular, result from either insertion or deletion that shifts the reading frame of the genetic code. Overall, substitution directly describes the process of one base being exchanged for another, making it the correct choice in this context.