Diagrammatic view of different types of AFE events. Alternative first exons are highlighted in orange and green. Constitutive exons are drawn in dark blue. Other alternatively spliced exons are drawn in brown. (A). Type I AFE clusters. Alternative first exons are mutually exclusive in different gene structures. (B). Type II AFE clusters. The first exon of one transcript is (part of) a downstream exon of other transcripts. (C). Some AFEs are coupled with downstream alternative splicing events.