Conservative patterns at the splice sites of introns in different phases. The Pr(identity) on y-axis stands for probability of identity at each position on the alignment. Positions 26 and 27 in the donor site correspond to GT, the terminal residues of the intron at the 5′ splice site, and positions 25 and 26 in the acceptor site correspond to AG, the terminal residues of the intron at the 3′ splice site. It can be seen that exonic regions not only are more conserved than intronic regions, but also display phase-dependent conservative patterns, which agree well with the preferred substitution in the third codon positions in the coding regions.
