Supernumerary marker chromosomes are characterized in the strategy proposed here (see Fig. 1) by different cyto­genetic, molecular cytogenetic and molecular methods, that have been described previously; GTG-banding, CBG- and NOR-staining are performed according to standard procedures [6].

Fluorescent in situ hybridization (FISH) including RNase- and pepsin-pretreatment, denaturation of the slides, and addition of the probe to the sample, were per­formed according to standard protocols [e.g., 7]. Cen-tromere-specific multicolor FISH (cenM-FISH) enables the one step characterization of all human centromeres and is described by Nietzel et al. [8]. AcrocenM-FISH is suited to the characterization of NOR-positive SMC [9]. The sub-cenM-FISH probe set consists of a centromere specific satellite probe, one centromere-near BAC in q and p (excluding the acrocentric chromosomes) and arm-specific pcp probes; sub-cenM-FISH can be used to char­acterize the peri-centric region in small SMC [10]. The multicolor banding (MCB) technique [11] can also be applied for that purpose in case of larger SMC [12-14]. Apart from the aforementioned molecular cytogenetic techniques, SMC can also be characterized by M-FISH [e.g., 15], microdissection [11] or micro-CGH [16]. The performance of microsatellite analyses is previously de­scribed [17-18].