Chromosome complement and location were examined by fluorescence microscopy for 225 meiotically mature (metaphase II) human oocytes after staining with DNA-specific probes. Both preovulatory oocytes and oocytes that failed to fertilize in vitro were analysed. After inspection in the living state, oocytes were selected for karyotyping or transmission electron microscopy. The findings demonstrate a high correlation between assessments of chromosome complement in living oocytes and the results from subsequent karyotypes. In addition to numerical aberrations (aneuploidy), the results also demonstrate the ability to detect abnormalities in chromosome structure and distribution. Specifically, this approach identified living oocytes that (1) contained no apparent chromosomes in the ooplasm, (2) contained chromosome not associated with the MII spindle and (3) had weak or no detectable chromosomal fluorescence in the first polar body. The findings demonstrate that approximately 8% of the oocytes were aneuploid (hypohaploid or hyperhaploid). Another 6.5% displayed anomalies in chromosome structure or distribution that could lead to aneuploid situations. The results are discussed with respect to the origin, occurrence and developmental consequences for such oocytes.

SUMMARYA newborn with an X/A translocation (46,X,der X,t(X; 17)(1 7pter-*-l7pl3::Xp22->Xqter) demonstrated multiple anomalies. X-replication studies in leukocytes of the patient with RBG (R Bands by BrdU using Giemsa stain) showed the abnormal X, t(X; 17), to be late replicating except for the translocated segment. Clinical findings and replication studies suggest failure of inactivation of the translocated segment.