**Core Concept**
The process of generating multiple proteins from a single gene is a fundamental concept in molecular biology, where a single gene can encode for different proteins through various mechanisms.

**Why the Correct Answer is Right**
Alternative splicing is the mechanism responsible for generating multiple proteins from a single gene. During transcription, a single gene can be transcribed into a pre-mRNA molecule that contains introns (non-coding regions) and exons (coding regions). The pre-mRNA is then processed by the spliceosome, which can remove different combinations of introns and exons, resulting in multiple mRNA transcripts with distinct coding regions. These transcripts can then be translated into different proteins, each with unique functions and properties.

**Why Each Wrong Option is Incorrect**
* **Option A:** Gene duplication is a process where a gene is copied and inserted into a new location in the genome, resulting in two identical copies of the gene. While gene duplication can lead to the evolution of new genes and proteins, it is not the mechanism responsible for generating multiple proteins from a single gene.
* **Option B:** Frameshift mutation is a type of genetic mutation that occurs when a single nucleotide is inserted or deleted from a gene, resulting in a shift in the reading frame of the genetic code. This can lead to the synthesis of a completely different protein, but it is not a mechanism for generating multiple proteins from a single gene.
* **Option C:** Gene expression is the process by which the information encoded in a gene is converted into a functional product, such as a protein. While gene expression can be regulated to produce different levels of a protein, it is not a mechanism for generating multiple proteins from a single gene.

**Clinical Pearl / High-Yield Fact**
Alternative splicing is a key mechanism that allows for the generation of protein diversity from a single gene, and it is estimated that approximately 90% of human genes undergo alternative splicing.

**Correct Answer: C. Alternative splicing.**