Chromosome micro-deletions and micro-duplications are an entity of cytogenetics well studied during the last few years thanks to the development of molecular cyto­genetic fluorescent in situ hybridization (FISH) tech­niques. Micro-deletions and micro-duplications of human chromosomes might not be seen, even by e most experi­enced cytogeneticist, if only the standard cytogenetic techniques are used such as GTG, QFQ, RHG bands, high resolution banding, etc. Fluorescent in situ hybridization, a combination of cytogenetic and molecular genetic tech­niques, was developed during the last two decades and is a powerful method of discovering submicroscopic chromo­some abnormalities. Most of these chromosome abnormali­ties are combined with certain phenotypic features, and in these cases, we speak about some well characterized ge­netic syndromes such as Williams, DiGeorge, Velocar­diofacial, Prader-Willi, Angelman, Pitt-Rogers-Danks, Miller-Dieker, Cri-du-Chat, Smith-Magenis, Wolf-Hirsch­horn, Beckwith-Wiedemann, Charcot-Marie-Tooth, etc.

Key words: Micro-duplications; Micro-deletions; Human chromosomes; Fluorescent in situ hybridization (FISH); Syndromes; Molecular cytogenetics; Clinical genetics.