Rearrangement of conserved linkage groups between D. melanogaster and D. pseudoobscura. The thick horizontal lines represent the chromosomal maps of the D. melanogaster and D. pseudoobscura Muller element C. Vertical lines drawn either down (D. melanogaster) or up (D. pseudoobscura) indicate conserved linkage groups. The locations and orientations of 80 breakpoint motifs are indicated with open and filled triangles at the junctions of conserved linkage groups. Diagonal lines connect homologous linkage groups in the two species where a single inversion event between breakpoint motifs will bring adjacent D. melanogaster genes together (dashed and gray lines). A second example that shows ectopic exchange between a pair of motifs where only one breakpoint brings adjacent D. melanogaster genes together is indicated with black solid lines.