Split decomposition graphs for all mouse Psg domain exons and rat PSG N1 domain exons for observed (Hamming) distances. Split decomposition analysis was performed using nucleotide sequences for individual groups of PSG domain exons. (A) N1 domain exons; (B) N2 domain exons; (C) N3 domain exons (the N4 domain exon of Psg24 is used instead of N3; see Fig. 3B in McLellan et al.  for explanation); (D) A domain exons. Numbers indicate respective PSG genes. Scale bars represent 0.01 (A) or 0.1 nucleotide substitutions per site (B, C, D).