Extensive, Recent Intron Gains in <i>Daphnia</i> Populations

Inserting Introns Introns—noncoding regions that interrupt coding gene sequences—are widespread throughout eukaryotic genomes, but intron gains and losses within and among species have been assumed to be rare. However, W. Li et al. (p. 1260 ) suggest that intron insertions can be relatively frequent within a population or species. By examining intron polymorphisms within genomes of different accessions of Daphnia pulpex (the water flea), and comparisons within the genus Daphnia , several instances of recent intron gains were observed, which appear to have occurred multiple times at the same site. Because intron insertions tend to be flanked by repetitive sequences, they may be the result of DNA damage repair mechanisms.