Merck, 11581074001, COT Human DNA

Repetitive elements (IRS) present in a probe (e.g., cosmids, YACs, chromosome painting probes) generate nonspecific hybridization signals that are distributed over the whole chromosome or genome. To enable specific hybridization of the probe to the chromosomal target site (e.g., single-copy sequences or low-copy repeats) the probe must be denatured in the presence of excess unlabeled COT Human DNA. This DNA serves as a competitor. In a subsequent preannealing step, the repetitive probe elements rapidly hybridize to excess repeats in the COT Human DNA, while most of the specific probe sequences remain single-stranded and thus can be hybridized to their chromosomal targets. This technique is known as chromosomal in situ suppression (CISS) hybridization.