Figure 4

Variability in OR gene polymorphism level. Cumulative number of OR genes (y axis) plotted against N values (x axis). The graph shows that more than 50% of OR genes are highly polymorphic, with an N value even smaller than that for anonymous sequences (see Table 6), whereas ~10% are barely polymorphic (N > 5000) (see additional file 2). Note that six OR genes with a very high N value were off-scale and were not plotted on this graph.