The discovery of RNA interference (RNAi) led to its use in biotechnology and medicine. All of the following are examples of how RNAi could be used in biotechnology or medicine, EXCEPT . a. to treat a disease characterized by a gene that is not expressed.
b. to study loss-of-function phenotypes of specific genes in a model research organism.
c. to treat a disease characterized by the buildup of a specific protein.
d. to treat a disease characterized by the overexpression of a nonmutated gene.
e. to treat a disease characterized by the normal expression of a mutated gene

a. to treat a disease characterized by a gene that is not expressed.

Explanation:

The RNA interference (RNAi) technique is widely used in molecular biology to inhibit target gene expression at the post-transcriptional level. The RNAi technology uses small interfering RNAs (siRNAs) consisting of 18-22 nucleotides that bind to complementary acid nucleics (i.e., DNA and RNA), thereby inhibiting target gene expression. Recently, it has interestingly been discovered that small RNA sequences targeting promoter regions can also be used to activate the expression of endogenous target genes through a mechanism called RNA activation (RNAa).