Why do genes have introns? Recombination might add a new piece to the puzzle

Much progress has been made recently regarding when and how spliceosomal in trons invaded eukaryotic genomes. Although the 'intron early-intron late' d ebate seems to be settled, the original and essential question remains: why have introns at all-do they have a purpose? Analyses of the relationship b etween intron length and recombination in Drosophila shed new light on the forces that drive the evolution of introns. Comeron and Kreitman proposed r ecently that introns are advantageous because they enhance within-gene reco mbination and therefore increase selection efficacy (Hill-Robertson effects ). However, their observations can also be explained by alternative neutral ist models.