Figure 1

Events of alternative splicing. In a typical alternatively spliced gene, where most of the exons are constitutive (i.e. they are always included in the final mRNA), four different types of alternative splicing events may occur to give rise to different final transcripts: a) cassette exons (one exon is skipped in some transcripts), b) isoforms of introns or exons (their boundaries may be different in different transcripts, with consequent truncation/extension of the flanking introns/exons), c) intron retentions (one intron is not spliced out and may be inserted into the final transcript), d) mutually exclusive exons (different exons may be included in different final transcripts). On the right of the figure the alternative mRNA transcripts are displayed; conserved parts are colored in green, while alternative elements are colored in red or blue.