MOLECULAR CYTOGENETIC CHARACTERIZATION OF BREAKPOINTS INVOLVING PERICENTRIC INVERSIONS OF HUMAN-CHROMOSOME-9

Pericentric inversions involving the secondary constriction (qh) regio n of chromosome 9 are considered to be normal variants. The evolutiona ry mechanisms and conservation of these inversions via Mendelian fashi on have been investigated since the advent of banding techniques. Rout ine cytogenetic techniques cannot provide the fine characterization ne cessary to determine the type of genetic material involved in these re arrangements. Therefore, the fluorescence in situ hybridization techni que with the human centromere-specific alpha satellite and the beta sa tellite (D9Z5) and classical satellite (D9Z1) human DNA probes were us ed to identify the breakpoints of chromosome 9 pericentric inversions. Four unique types of pericentric inversions involving the 9qh region were observed, and the mechanism may be due to breakage and reunion at the proposed breakpoints. They are: type A inversions consist of brea kpoints within the alpha and beta satellite DNA regions; type B consis t of breakpoints within the beta satellite DNA region and band 9q13; t ype C involve breakage within the beta and classical satellite DNA reg ions, and type D have breakpoints within the alpha and classical satel lite DNA regions. Obviously, reshuffling of satellite DNA sequences ha s occurred, which has given rise to a variety of heteromorphisms whose clinical significance remains obscure.