Figure 3

Construction of the breakpoint graph for a circular genome I and a general genome A. The adjacencies of I are represented by black edges and those of A by grey edges. Unvisited nodes are white, visited ones are black. We can create a cycle only when e (the number of unvisited nodes) is even (a). We can merge two paths when e is even (b) or odd (d). We can skip a vertex when e is even (c) or odd (e). In (c) and (d), the parity of the number of unvisited vertices is changed.