In order to develop an understanding of the evolutionary history of introns,
we compared intron sequences from homologous genes of different vertebrate
species. We observed the following statistical features of introns.
From interspecies comparisons, the length difference of an intron from
each gene exhibits considerable variations, which is in consistent with
the previous observation on the wide distribution of insertion and deletion
sizes. The distribution profiles also indicate that 68% of introns are
longer in human than in rodentia, although such a significant shift in
the intron length is not observed in mousek/rat and human/artiodactyla
comparisons. From the analysis of diversities in base compositions and
sequence data between intron and coding regions, a similar behavior was
observed between intron and the third codon position, although intron
sequences appeared to be more constrained. Those descriptive analysis
will help us to understand the functional constraints and the recent
history of introns.