Locus-specific probes target a specific gene sequence of interest. These probes can determine whether a gene is amplified, deleted, or present in a normal copy number.
The number of centromeres usually determines amplification in the same cell. The ratio of the gene to centromere number is frequently used to report whether a tumor is amplified or deleted for a particular gene.
The optimal way to determine if a gene is genuinely amplified is to have a probe set with both the locus-specific probe and the centromere probe for the same chromosome. This procedure is used in many types of FISH testing, such as:
- Human epidermal growth factor receptor 2 (HER2/neu)
- Epidermal growth factor receptor (EGFR)
- Myelocytomatosis cellular oncogene (C-MYC)
Deletion involves the loss of a segment of a chromosome.
In the image, the chromosome on the left contains 1 copy of a gene (locus-specific probe) that is tagged with a red fluorescent dye and would be read as 1 red signal. The chromosome on the right contains 3 copies of a gene (locus-specific probe) that is tagged with a red fluorescent dye and would be read as 3 red signals.
