Distribution of the different types of alternative splicing events. The percentage and total number (in parenthesis) of splicing events is shown for each type of alternative splicing, i.e., intron retention (IR), exon skipping (ES), alternative 5′ splice site (Alt5′) and alternative 3′ splice site (Alt3′). Asterisks (*) indicate the percentage of other, more complex alternative splicing types. The distribution is given for the species Volvox (A), Chlamydomonas (B), Arabidopsis (C) and human (D). The total number of alternative splicing events is 580 in Volvox, 493 in Chlamydomonas and 9,343 in Arabidopsis.