Chromosome rearrangement has been considered to be important in the evolutionary process. Here, we demonstrate the evolutionary relationship of the rearranged human chromosome 12 and the corresponding chromosome XII in apes (chimpanzee, bonobo, gorilla, orangutan, and gibbon) by examining PCR products derived from the breakpoints of inversions and by conducting shotgun sequencing of a gorilla fosmid clone containing the breakpoint and a "duplicated segment" (duplicon). We confirmed that a pair of 23-kb duplicons flank the breakpoints of inversions on the long and short arms of chimpanzee chromosome XII. Although only the 23-kb duplicon on the long arm of chimpanzee chromosome XII and its telomeric flanking sequence are found to be conserved among the hominoids (human, great apes, and gibbons), the duplicon on the short arm of chimpanzee chromosome XII is suggested to be the result of a duplication from that on the long arm. Furthermore, the shotgun sequencing of a gorilla fosmid indicated that the breakpoint on the long arm of the gorilla is located at a different position 1.9 kb from that of chimpanzee. The region is flanked by a sequence homologous to that of human chromosome 6q22. Our findings and sequence analysis suggest a close relationship between segmental duplication and chromosome rearrangement (or breakpoint of inversion) in Hominoidea. The role of the chromosome rearrangement in speciation is also discussed based on our new results.