Chromosomal rearrangements detected by PGI. Four rearrangements detected by PGI were confirmed by direct sequencing of BACs. The direct sequencing confirmed that each of the BACs mapped to two chromosomal locations in human. Mappings of one of the four BACs, denoted CH250-272A22, indicate either an interchromosomal rearrangement or BAC chimerism; CH250-268B13 and CH250-268E11 span tandemly duplicated regions on chromosome 16; CH250-268P6 (enlarged on the right) spans a 254-kbp interchromosomal duplication in human. By using mouse and rat as outgroups for chimpanzee and human, one can hypothesize that the duplication occurred in the human lineage after the branching of chimpanzee.