Evolution versus constitution: differences in chromosomal inversion

We compared the chromosomal breakpoints of evolutionary conserved and constitutional inversions. Multicolor banding and human- specific bacterial artificial chromosomes were applied to map the breakpoints of constitutional pericentric inversions on human chromosomes 2 and 9. For the. first time, we present a highresolution analysis of the breakpoint regions, which are characterized by gene destitution, co- localization with fragile sites, multitude repeats as well as pseudogenes and, remarkably, a large sequence homology to the opposite breakpoint. In contrast, evolutionary inversion breakpoints lack such extensive cross- hybridizing regions and are often associated with fragile sites of the genome and low- copy repeats. These molecular characteristics gave evidence for different types of inversion formation and indicate that evolutionary inversions cannot originate from constitutional inversions like those of chromosomes 2 and 9. Finally, the constitutional inversion breakpoints were investigated on three different great ape species and on four test persons each bearing the same cytogenetically determined inversion on chromosomes 2 and 9, respectively. Our data indicate the existence of different molecular breakpoints for the two variant chromosomes.