Fiber-FISH: fluorescence in situ hybridization on stretched DNA.

High-resolution fluorescence in situ hybridization (FISH) on deproteinized, stretched DNA prepared by in situ extraction of whole cells immobilized on microscope glass slides allows the visualization of individual genes or other small DNA elements on chromosomes with a resolution of approx 1000 bp. Applications of fiber-FISH range from the determination of numbers of repetitive genes to establishing the physical order of cloned DNA fragments along continuous sections of individual chromosomes. Particularly in organisms with relatively small and gene dense genomes, such as protozoan parasites, fiber-FISH can easily be used as a complementary technique to classical in vitro mapping approaches.