What is the result of alternative RNA splicing in eukaryotic gene expression?

• A. Long DNA sequences
• B. Several mRNA isoforms from a single gene
• C. Inactivation of gene expression
• D. Removal of exons rather than introns

Answer: (B)

Alternative RNA splicing changes which parts of the pre-mRNA are kept in the final mRNA. In eukaryotes, after transcription, the spliceosome removes introns and joins exons together. By including or skipping different exons, a single gene can produce several distinct mRNA isoforms. These different transcripts can be translated into different protein variants, increasing the diversity of proteins a single gene can encode without changing the underlying DNA sequence. The other ideas don’t fit because DNA length isn’t altered by splicing, and splicing usually yields functional protein products rather than simply inactivating the gene. Also, while introns are removed, the hallmark of alternative splicing is the selective inclusion or skipping of exons, not removal of exons.