Final answer:
The FISH analysis with a break-apart probe showing three signals in 30% of the nuclei suggests that a translocation is present in those cells, as the separated signals indicate the probes binding to different chromosomal locations.
Step-by-step explanation:
Fluorescent in situ hybridization (FISH) is a powerful tool in cytogenetics that enables the detection of chromosomal rearrangements, such as translocations, using fluorescently labeled DNA probes. In a FISH analysis, a break-apart probe is designed to bind to specific chromosomal regions that are known to be involved in a translocation. Under normal circumstances, without a translocation, the fluorescent signals from the probes should be adjacent or overlapping, appearing as one or two combined signals. However, if a translocation is present, the probe's target regions will be separated, leading to separate signals.
Based on the FISH analysis described, where 70% of the nuclei showed two signals and 30% showed three signals, it seems that a portion of the cells have undergone a translocation. Normally, cells should show two combined signals, representing the undisturbed state of the chromosomal regions of interest. The presence of three distinct signals in 30% of the nuclei indicates that the break-apart probes have bound to separate locations, consistent with a chromosomal translocation event.
It is important to interpret these results in the context of the specific case and clinical history, but the FISH analysis described suggests the occurrence of a chromosomal translocation in a significant proportion of the cells analyzed.