Learning Objective: At the end of this lesson, the learner will be able to describe the principle, procedure, and clinical applications of FISH and identify chromosomal abnormalities detectable by this technique.
Fluorescence In Situ Hybridization (FISH) is a cytogenetic technique that uses fluorescently labeled DNA or RNA probes to detect and localize specific sequences on chromosomes.
FISH is especially useful for visualizing chromosomal anomalies that may not be detectable with standard karyotyping, including:
- Microdeletions
- Duplications
- Translocations
- Aneuploidy
Principle and Procedure
- Sample preparation: Cells are fixed onto a slide.
- Probe hybridization: Fluorescent DNA or RNA probes complementary to the target sequence are added.
- Visualization: Bound probes are detected using fluorescence microscopy, revealing the location and number of specific sequences.
Detection of Chromosomal Abnormalities
| Abnormality | FISH Observation | Example / Notes |
|---|---|---|
| Microdeletion | Lack of fluorescence signal on one chromosome copy | Detects small deletions invisible on karyotype |
| Translocation | Fluorescence at an unexpected location | E.g., t(17;19) in cancer cells |
| Duplication / Aneuploidy | Additional fluorescent signals | Extra copy of chromosome 8 → trisomy or tetrasomy |
| Gain / Loss | Change in the number of signals | Detects monosomy or trisomy for specific chromosomes |
Clinical Applications
- Cancer cytogenetics: Detect oncogene amplifications or translocations
- Prenatal diagnosis: Detect microdeletion syndromes (e.g., DiGeorge syndrome 22q11 deletion)
- Genetic disorders: Confirm copy number variations, duplications, or deletions
- Research: Study gene localization and chromosomal organization
Advantages Over Karyotyping
- Detects smaller structural changes not visible on the standard metaphase karyotype
- Faster and more targeted
- Can be applied to interphase cells, not requiring mitotic arrest
