Two Genomes and their Breakpoint Graph. (a) Genomes π and Γ on a collection of 12 genes. We use “h” and “t” to denote the head and tail of a gene. π is drawn with blue adjacencies, and Γ is drawn with red adjacencies. (b) The breakpoint graph of π and Γ. We have labeled the endpoint v of a path with π if v is π-open, with Γ if v is Γ-open, and with ∅ if v is a telomere of at least one genome.