The origin of small supernumerary marker chromo­somes (SMC) is nearly impossible to establish by routine cytogenetics alone, while fluorescent in situ hybridization (FISH) methods are highly suited for that purpose. How­ever, a 24-color-FISH approach, using whole chromosome painting (WCP) probes, can only be used successfully for the determination of the marker’s chromosomal origin if it is larger than 17p, thus, smaller SMC found in clinical cytogenetics in 0.01-0.05% often cannot be characterized. This paper suggests a strategy for the characterization of small SMC using recently established methods such as centromere specific multicolor FISH (cenM-FISH) or multicolor banding (MCB).

Key words: Supernumerary marker chromosomes (SMC); Fluorescent in situ hybridization (FISH); Strategy for characterization, Uniparental disomy (UPD).