FISH Probes
Fluorescent in situ hybridization (FISH) is a cytogenetic technique used to detect genes or chromosomal regions in a DNA sample. FISH probes are composed of a fluorescent tag attached to a DNA fragment complementary to the DNA sequence being targeted. When added to the sample, the probe will hybridize to its complementary strand, appearing as a fluorescent signal. FISH probes can be used to detect several types of genetic alterations. Different probe types are used to identify different abnormalities:
Control
Control probes are used for both chromosome enumeration and verifying that copy number variation probes have hybridized to the correct chromosome. Fewer or greater than two signals (one for each sister chromosome) will indicate chromosome aneuploidy.
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Copy Number Variation
Copy number variation probes are used to detect gene amplifications and deletions. They’re made of one probe designed to hybridize to a single gene. Extra or missing signals will indicate gene gains or losses.
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Break Apart
Break apart probes are used to detect gene translocations. They’re composed of two probes, each bordering one end of the gene. If the gene has rearranged from its typical location, the two probes will split, appearing as two unique signals.
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Fusions
Fusion probes are used to detect fusions between two typically separate genes. They’re made of two probes, each designed to hybridize to its respective gene. If the genes have fused, the probes will appear as one unified signal.
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