The construction of GTNs and how GTNs are affected by evolutionary events. (A) Constructing a GTN from a genome. Supposing that Gene1 and Gene3 are annotated as COGA, Gene2 as COGB and Gene4 as COGC, the numbers adjacent to the lines in the GTNs are degrees. (B) The variation in GTN structure when Gene1 is duplicated and inserted between GeneX and GeneY. GeneX and GeneY are annotated as COGX and COGY, respectively. (C) The variation in GTN structure when Gene1 is lost. (D) The variation in GTN structure when the segments of Gene2 and Gene3 are reversed in the genome.