Two-color hybridization with high complexity chromosome-specific probes and a degenerate alpha satellite probe DNA allows unambiguous discrimination between symmetrical and asymmetrical translocations.

This report describes a fluorescence in situ hybridization approach to chromosome staining that facilitates detection of structural aberrations and allows discrimination between dicentric chromosomes and symmetrically translocated chromosomes. In this approach, selected whole chromosomes are stained in one color by hybridization with composite probes whose elements have DNA sequence homology along the length of the target chromosomes. In addition, all chromosomes are counterstained with a DNA specific dye so that structural aberrations between target and non-target chromosomes are clearly visible. Discrimination between dicentric chromosomes and symmetrical translocations is accomplished by hybridization with a second probe that is homologous to DNA sequences found in the centromeric region of all chromosomes. The centromeric marker is visualized in a different color, so that the number of centromeres per aberrant chromosome can be rapidly determined in the microscope by changing excitation and fluorescence filters.