alternative splicing

Alternative splicing is how one gene becomes a wardrobe of outfits instead of a single garment. By keeping some exons and skipping others, a cell can assemble different mRNAs from the very same gene, and so build several related proteins — each suited to a particular tissue, stage, or job.

During splicing, the cell does not always make the same cuts. It may include an exon in one cell type and omit it in another, lengthen or shorten an exon, or even keep part of an intron. Regulatory proteins that bind the RNA guide these choices, responding to the cell's identity and signals. The result is that the number of distinct proteins an organism can make far exceeds its number of genes.

This flexibility is a major source of biological complexity, especially in animals, where a large fraction of genes are spliced in more than one way. It is also a vulnerability: mutations that change which exons are included can produce faulty proteins, and disrupted splicing contributes to a range of inherited diseases and cancers.