What is alternative splicing and why is it significant?

Alternative splicing is a process where different combinations of exons are joined together during mRNA processing, allowing one gene to produce multiple protein isoforms. Types include exon skipping, alternative 5' or 3' splice sites, intron retention, and mutually exclusive exons. Over 95% of human multi-exon genes undergo alternative splicing, greatly expanding proteome diversity beyond gene number. Splicing is regulated by splicing factors (SR proteins, hnRNPs) responding to cellular signals. Dysregulation causes diseases including cancer and neurological disorders. It explains how ~20,000 genes can encode >100,000 proteins.