Inversion Signatures. The figure shows two regions with inversion signatures. The region a1–a2 in the draft genome matches regions b1 and b3 in the reference genome. b1 and b3 are not consecutive in the reference genome and hence this defines a breakpoint; moreover, because the match between a1 and b1 has a diffferent orientation as compared to the match between a2 and b3 this breakpoint is an inversion signature. The same happens with region a3–a4 of the draft genome and regions b2 and b4 of the reference genome. Both ISs are related because they are the result of the same inversion event. Therefore these two ISs constitute an IS pair.