Children with clinical features suggestive of monosomy 1p36 may be tested for a deletion of 1p36 by FISH simultaneously with high-resolution chromosomal analysis. FISH (fluorescence in-situ hybridization) is a process which vividly paints chromosomes or portions of chromosomes with fluorescent molecules. FISH provides researchers with a way to visualize and map the genetic material in an individual's cells, including specifc genes or portions of genes.

FISH works by the researcher preparing short sequences of single-stranded DNA that match a portion of the gene the researcher is looking for. These are called probes. The next step is to label these probes by attaching one of a number of colors of fluorescent dye.  DNA is composed of two strands of complementary molecules that bind to each other like chemical magnets. Since the researchers' probes are single-stranded, they are able to bind to the complementary strand of DNA, wherever it may reside on a person's chromosomes. When a probe binds to a chromosome, its fluorescent tag provides a way for researchers to see its location.
 
FISH is a rapid, reliable and direct approach for identifying patients with microdeletions or microduplications. Unlike most other techniques used to study chromosomes, FISH does not have to be performed on cells that are actively dividing. This makes it a very versatile procedure.