SEQUENTIAL IMMUNOCYTOGENETICS, MOLECULAR CYTOGENETICS AND TRANSMISSION ELECTRON-MICROSCOPY OF MICROSPREAD MEIOSIS-I OOCYTES FROM A HUMAN FETAL CARRIER OF AN UNBALANCED TRANSLOCATION

The oocytes of a 17 week human fetus carrying an unbalanced 46,XX,add( 18)(p13) translocation were studied with a sequential combination of m icrospreading, immunocytogenetics, fluorescence in situ hybridization (FISH) and transmission electron microscopy. This combination of techn ologies allowed the collection of data of unique accuracy and resoluti on. The translocated chromosome was found to be involved in five diffe rent synaptic configurations. A consistent feature of these configurat ions was the involvement of a second small bivalent, presumably chromo some 21 or 22, the normal synapsis of which was often disrupted. We co nclude that chromosome 21 or 22 was the source of the translocated mat erial, which was found to be either homologously triply synapsed, hete rologously synapsed or asynapsed.