Figure 6

Intron presence and ancientness of gene sequence. A. Average number of identical residues in the homology regions between sequence pairs as a function of the length of identical residues (x) around the (virtual) splice site. Sequences with a splice site were compared with control sequences without a splice site (cf. Fig. 5A and B). Maximum number of identical residues is 20, representing 100% similarity in this region. Error bars represent standard deviation with N = 650 (x = 1), N = 564 (x = 2), N = 34 (x = 3), N = 11 (x = 4) and N = 27 (x = 5), and for the control N = 267, 695, 199, 60 and 65, respectively. B. The same data set as in A, but now the percentage of conserved sequences as a function of number of fixed identical residues is shown. Conserved sequences were defined as having 6 or more identical residues (apart from the identical residues in the splice site; red in Fig. 5) in the two regions of homology (black in Fig. 5), dividing the data in a non-conserved and a conserved gene set. Cf. Fig. 5C where the first 2 sequences would be considered non-conserved, and the last 3 would be conserved.