Fig. 4

Checking whether gene X from R has an ortholog X*′ in upper species A through a fish genome F that involves, e.g., two witnesses. Here, R is a fixed reference species; gene X has the ortholog X* in fish F confirmed by two witness pairs, Y–Y* and Z–Z*. The gene X* in turn has the ortholog X*′ in upper species A confirmed by two witness pairs, V–V′ and T–T′. The dashed arrow represents the α-homology condition, and the solid arrow represents the β-homology (see for the determination of α- and β-homology Step 2 in section A of Methods). The brackets indicate the chosen neighborhoods with radii r, in which the witnesses are sought. The witnesses may be arbitrarily positioned and directed within the neighborhood