Lactose permease is encoded by the lacY gene of the lac operon. A mutation occurred at codon 64 that changed the normal glycine codon into a valine codon. The mutant lactose permease is unable to function. However, a second mutation, which changes codon 50 from an alanine codon to a threonine codon, is able to restore function. Are the following terms appropriate or inappropriate to describe this second mutation?
A. Reversion
B. Intragenic suppressor
C. Intergenic suppressor
D. Missense mutation