INTRONS AND EXONS

Analysis of the exon-intron structures of genes, and a survey of the e volutionary distribution of mosaic proteins suggest that modularizatio n of protein domains by intron insertions and their dispersal through exon-shuffling become significant on ly in higher eukaryotes. The appe arance of this powerful evolutionary mechanism probably contributed si gnificantly to the 'Big Bang' of metazoan radiation.