DIRECTION OF DNA-SEQUENCES WITHIN CHROMATIDS DETERMINED USING STRAND-SPECIFIC FISH

The 5' to 3' direction of DNA strands within chromatids of metaphase c hromosomes can be determined by using simultaneous hybridization of a single strand of the telomere probe and a single strand of a repetitiv e sequence to slides pretreated for strand-specific hybridization. The telomere probe identifies the direction of the DNA helical strand rem aining in each chromatid of the metaphase chromosomes. The direction o f the repetitive sequence is then determined from the direction of the strand to which it hybridizes. This method was used to determine the 5' to 3' direction of three repetitive DNA sequences, each for a diffe rent human repeat family.