Fig. 8.

Evolution of the clade B serpins. The model shows serpin genes as blue (seven-exon genes) or orange (eight-exon genes) block arrows. Shown, starting at the bottom, is the ancestral locus with a single seven-exon gene, followed by subsequent stages to generate the ancestor locus of birds and mammals deduced in Fig. 6 and shown here at the top. Within the tetrapod lineage, the asterisk (*) represents an event in which additional sequence, including a CD loop, was added within a seven-exon gene, generating an eight-exon gene. Further details are in the text.