ANALYSIS OF SEX-CHROMOSOME DISTRIBUTION IN THE GONADAL TISSUE OF A 45,X 47,XYY MOSAIC BY FLUORESCENCE IN-SITU HYBRIDIZATION/

45,X/47,XYY mosaicism is a rare condition with scarce information on t he tissue specific distribution of the different cell lines. Fluoresce nce in situ hybridization with repetitive, chromosome-specific DNA pro bes was applied to gain insight into the tissue specific distribution of the two cell lines in biopsies of the streak gonad and dysgenetic t estis of a a-year-old individual exhibiting 45,XI 47,XYY mosaicism. Th e distribution of the 45,X/47,XYY cells within different tissues was f ound to be nonrandom. The coelomic epithelium, the vascular endotheliu m, and the prepuberal germ cells exhibited predominantly a 47,XYY kary otype. In contrast, Sertoli cells exhibited both karyotypes, and the r emaining tissue was predominantly composed of 45,X cells. The contribu tion of the two cell lines to gonadal development is discussed.