Distribution of domain gain events according to the position of domain insertion and number of exons gained. Gains at amino and carboxyl termini and in the middle of proteins are shown separately. The first column in each group shows the fraction of gains where the gained domain is coded by multiple new exons and the second where it is coded by a single new exon. The third column shows the fraction of gains where the ancestral exon has been extended and the gained domain is coded by the extended exon as well as by additional exons. Finally, the fourth column in each group shows cases where only the ancestral exon has been extended with the sequence of a new domain.