Figure 1

Gene structure-based phylogenetic classification of vertebrate serpins. Positions of introns refer to the human α₁-antitrypsin sequence. A two amino acid indel present between positions 173 and 174 (α₁-antitrypsin numbering) suggests that groups 1, 3, and 5 are more closely related to each other than to the other groups. Gene groups 2, 4, and 6 lack the 173/174 indel and depict an intron at position 192a, implying shared ancestry. Some group 1 members contain an additional intron at position 85c (not shown). For further details see references 20 and 21.