Depending on the number of paralogs of a given cancer gene at each branch, we also derive the corresponding orthology ratio, defined as the number of co-orthologs of that human gene in a given lineage. This ratio provides a useful indication of the number of intra-lineage duplications that the gene underwent during evolution. Orthology ratio can be 1 to 1 when no duplications occurred; 1 to N, indicating one-to-many relationship; N to 1, corresponding to many-to-one relationship; N to N, when multiple duplications occurred during evolution.
