Fluorescent in situ hybridization (FISH)
Using Fluorescent-labelled DNA probes which are designed that are complementary to the DNA sequences being assessed, to detect and localize the presence or absence of specific DNA sequence on Chromosome.
Steps:
ü Chromosomes are immobilized and denatured on a microscope slide and exposed to a solution containing a fluorescently labelled probe specific to a specific chromosomal region.
ü After hybridization (the formation of a double strand of DNA from complementary single strands), the slide is washed and examined microscopically.
ü Where the probe has hybridized, fluorescent spots are seen over the relevant chromosome.
For example, if a child were suspected of having 22q11 deletion syndrome, FISH using a 22q11-specific probe would show only one pair of fluorescent spots, rather than two.
Types of FISH probes:
ü Centromeric (aneuploidy)
ü Telomeric (subtelomeric rearrangements)
ü Sequence specific (microdeletions)
ü Whole chromosome paint (complex rearrangements)
ü Reverse painting (to identify origin of unidentified chromosomal material)
Useful for microdeletion syndromes.