EVOLUTION OF THE INTRON-EXON STRUCTURE OF EUKARYOTIC GENES

The origin and evolution of intron-exon structures continue to be cont roversial topics. Two alternative theories, the 'exon theory of genes' and the 'insertional theory of introns', debate the presence or absen ce of introns in primordial genes. Both sides of the argument have foc used on the positions of introns with respect to protein and gene stru ctures. A new approach has emerged in the study of the evolution of in tron-exon structures: a population analysis of genes. One example is t he statistical analysis of intron phases-the position of introns withi n or between codons. This analysis detected a significant signal of ex on shuffling in the DNA sequence database containing both ancient and modern exon sequences: intron phase correlations, that is, the associa tion together within genes of introns of the same phase. The results o f this analysis suggest that exon shuffling played an important role i n the origin of both ancient and modern genes.