Small supernumerary marker chromosomes (sSMC) are still a major problem especially in prenatal cytogenetic diagnostics and counseling. These structurally abnormal chromosomes cannot be identified or characterized unambiguously by conventional banding cytogenetics alone, and are generally about the size of or smaller than a chromosome 20 in the same metaphase spread. We describe a straightforward algorithm, based on data from 2,211 reported cases (http://www.markerchromosomes.ag.vu) to quickly characterize the sSMC’s chromosomal origin.

__________________________________________________

             2 Institute of Cytology and Genetics, Novosibirsk, Russia

             3 Institute of Hereditary Diseases, Minsk, Belarus