ALTERNATIVE SPLICING “is a process by which exons or portions of exons or noncoding regions within a pre-mRNA transcript are differentially joined or skipped, resulting in multiple protein isoforms being encoded by a single gene. This mechanism increases the informational diversity and functional capacity of a gene during post-transcriptional processing and provides an opportunity for gene regulation.”
http://bitesizebio.com/10148/what-is-alternative-splicing-and-why-is-it-important/