Seven closely related isolates of Candida albicans exhibited progressive decreases in susceptibility to posaconazole. Sequencing of the gene involved in azole resistance in these strains revealed predicted proteins with single amino acid changes. Which of the following best describes the type of mutation that has resulted in decreased susceptibility to posaconazole in these strains?

The mutation described here is a missense mutation (c), or one in which base substitution resulting in a codon that causes a different amino acid to be inserted. Mutations result from three types of molecular changes, namely, base substitution mutation, frameshift mutation, and transposon or insertion sequences causing mutations. Inversion mutations (b) are caused by insertion sequences (ISs) or IS-like elements. Missense mutation (c) refers to base substitution resulting in a codon that causes a different amino acid to be inserted. Nonsense mutation (d) refers to base substitution generating a termination codon that prematurely stops protein synthesis. Replacement mutations (e) are transition or transversion depending on the substitution. Transition mutations are the replacement of a pyrimidine (C, T) by a pyrimidine or a purine (A, G) by a purine. Transversions (e) are the replacement of a purine by a pyrimidine or pyrimidine by a purine.