Some novel intron positions in conserved Drosophila genes are caused by intron sliding or tandem duplication

Background Positions of spliceosomal introns are often conserved between remotely related genes. Introns that reside in non-conserved positions are either novel or remnants of frequent losses of introns in some evolutionary lineages. A recent gain of such introns is difficult to prove. However, introns verified as novel are needed to evaluate contemporary processes of intron gain.