A) cenM-FISH identified the sSMC as a derivative of chromosome 20 (arrowhead). The asterisk besides chromosome 10 indicate that one chromosome is lacking here due to preparation artifacts. B) subcenM-FISH with a chromosome 20 specific probe set revealed the presence of three different types of marker chromosomes besides two normal chromosomes 20, i.e. either a ring (r(20)), a double ring (r(20;20)) or an inverted duplicated dicentric minute chromosome 20 (min(20;20)). C) A BAC probe specific for 20p12.2 showed a signal only in the r(20) but not on r(20;20) or min(20;20). Thus, a final karyotype of r(20)(::p12.2~12.3->q11.1::)/r(20;20)(::p12.1->q11.1::q11.1->p12.1::)/min(20;20)(:p12.1->q11.1::q11.1->p12.1:) for the marker chromosome was defined.