Here is one example of the tracking of intron position between homologous yeast genes. Intron position was defined at the nucleotide level making it possible to determine whether the intron is at an identical position (same codon and same phase) or not in the homologues. CLUSTALX multiple alignments were performed to help these comparisons and the reconstruction of a virtual (scaffold) YNR053c gene, exhibiting the probable ancestral intron arrangement.
This example clearly shows that the i1 intron position has been evolutionary conserved at an identical position from S. pombe to S. cerevisiae, and is probably a relics of an ancestral position [Bon et al., 2003].
It is noteworthy that orthologous introns are not highly constrained in sequence.