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Inference of Genotype–Phenotype Relationships in the Antigenic Evolution of Human Influenza A (H3N2) Viruses

Figure 2

Schematic drawing demonstrating the up/down tree concept.

For the two taxa t2 and t4, no antiserum is present, and thus, b3 and b6 only have up-weights. A path from t1 to t3 would use the up-weights of branch b1 and b2, and the down-weights of branch b4 and b5. Similarly, the path from t2 to t1 would use the up-weight of branch b3 and the down-weight of branch b2. Notably, the path from t1 to t1, namely the antigenic distance from antigen t1 to the antiserum raised against strain t1, would use the up-weight and the down-weight of branch b1.

Figure 2