Dicentric chromosome: An abnormal chromosome with two centromeres rather than the normal one. Every normal chromosome has one centromere that tethers it to the pole of the spindle and is essential to the chromosome at the time of cell division. However, a dicentric chromosome is doubly tethered (by its two centomeres) and is pulled to the opposite poles of the spindle when the cell divides, causing the chromosome to break. The broken ends of the chromosome fuse with each other in the daughter cell and form a new dicentric chromosome. Dicentric chromosomes therefore lead to chromosome instability. This remarkable sequence of events was discovered by Barbara McClintock in 1941 who studied dicentric chromosomes in maize (corn) and later won a Nobel Prize.