Fluorescence in situ hybridization (FISH) testing. A test of DNA (deoxyribonucleic acid) designed to identify the presence of genetic defects in a person or, usually, a fetus. In a genetic probe, a particular fragment of DNA is examined for genetic markers, specific base sequences (chemical configurations) that have been associated with a genetic defect. Genetic probes can be used to detect the presence of Down syndrome, cystic fibrosis, trisomy 21 syndrome, and such chromosomal abnormalities as Turner syndrome.
A particular segment of DNA is employed in laboratory examinations to ascertain the presence of a specific genetic defect within an individual’s DNA. This segment, known as the “probe,” possesses an identical structure to the abnormal gene. When introduced to a sample of the person’s DNA, the probe will attach itself to the gene if it is present. To facilitate easy detection, a radioactive or fluorescent marker can be incorporated into the probe.
Genetic probes find primary application in antenatal diagnosis of genetic disorders, as well as in identifying whether individuals with a family history of such disorders harbor the faulty gene themselves.