Robertsonian translocations (ROBs) are the most common rearrangements in humans, 
contributing significantly to genetic imbalance, fetal wastage, mental 
retardation and birth defects. Rob(14q21q) and rob(13q14q), which are formed 
predominantly during female meiosis, comprise the majority (approximately 85%) 
of all ROBs. Previous studies have shown that the breakpoints are consistently 
located within specific regions of the proximal short arms of chromosomes 13, 
14, and 21. The high prevalence of these translocations, the consistent 
breakpoints found, and the fact that roughly 50% of cases occur sporadically 
suggest that the sequences at or near the breakpoints confer susceptibility to 
chromosome rearrangement and that the rearrangements occur through a specific 
mechanism. To investigate this hypothesis, we developed hamster-human somatic 
cell hybrids derived from de novo rob(14q21q) patients that contained the 
translocated chromosome segregated from the other acrocentric chromosomes. We 
determined the physical order of five satellite III subfamilies on 14p, and 
investigated their involvement in formation of these de novo translocations.