Exonization of transposed elements: A challenge and opportunity for evolution

► We review strategies to reconstruct the evolution of novel exons (exonization). ► Main emphasis on special case of transposed Short INterspersed Elements (SINEs). ► Phylogeny is the basis for the chronology of events leading to exonizations. ► Novel exons mostly alternatively spliced, RNA editing or constitutive splicing rare. ► Persistent exonization requires long evolutionary periods.