EXTREME VARIANT OF THE SHORT ARM OF CHROMOSOME-15

Using fluorescence in situ hybridization, primed in situ labelling, an d conventional cytogenetic staining we have characterized an excessive ly enlarged short arm of chromosome 15. The likely mechanism explainin g this variant chromosome involves amplification of rDNA sequences fol lowed by inverted insertional translocation between the enlarged siste r chromatids of the short arm of chromosome 15.