How does FISH detect missing pieces of chromosomes?

Fluorescence in situ hybridization (FISH) detects missing pieces of chromosomes by utilizing fluorescently labeled probes that are designed to bind to specific DNA sequences.12

When these probes are applied to a sample, they seek out and attach to their complementary target sequences on the chromosomes. If a specific segment of a chromosome is missing—a condition known as a deletion—the corresponding fluorescent probe will have no target to bind to at that location. By examining the chromosomes under a fluorescence microscope, researchers can identify the absence of a fluorescent signal where it would normally appear, thereby confirming the presence of a genetic deletion.123

This technique is highly sensitive and specific, allowing for the detection of small deletions involving as few as one to five genes, as well as larger structural abnormalities. Because it does not require cell culture, FISH provides results more rapidly than traditional karyotyping, making it a valuable tool in clinical genetics and preimplantation genetic diagnosis.132