Alternative Splicing

A single gene can contain numerous exons and introns, and the exons can be spliced together in different ways. For example, if a gene contains 10 exons, one version of the mRNA transcribed from that gene might contain exons 1-9. Another version of the mRNA might contain exons 1-8, and exon 10. This is called alternative splicing, and can produce different forms of a protein from the same gene. The different forms of the mRNA are called transcript variants, splice variants, or isoforms.

Please see also the excellent illustration of alternative splicing in figure 2 of "Genomic medicine--a primer," by AE Guttmacher and FS Collins. (PubMed; Full Text available at the New England Journal of Medicine.)