What can be inferred if a single control signal is consistently absent across all cells during a FISH test?

If a single control signal is consistently absent across all cells during a FISH (Fluorescence In Situ Hybridization) test, it suggests that there may be a deletion of a specific genomic region linked to the control signal. In FISH testing, control signals are vital for verifying the successful hybridization of the probe and the integrity of the target genomic region. If a control signal, which is expected to be present, is missing in all analyzed cells, it indicates that the corresponding genomic sequence is likely missing or deleted. This consistent absence points to a structural alteration in the chromosome, such as a deletion, that has affected the targeted region, causing the control signal to not be detected.

While other options may seem plausible, such as the potential for a non-essential control signal or technical issues, the key takeaway is that a systematic absence of the control signal across all cells most strongly indicates a specific genomic deletion, confirming that the genomic region in question is no longer present.