What is the difference between fusion-signal FISH and split-signal FISH?

Although both strategies are commonly used to detect gene translocations, they are different in principles and data exhibition. In fusion-signal FISH, two differentially labeled probes, e.g., green and red, are used to flank the breakpoint regions of the two genes involved in the translocation. In normal cells, separate red and green signals are observed, while in case of a translocation, a yellow signal which is colocalized from the green and red signal will be observed. The split-signal FISH also uses two differentially labeled probes, but these probes are located in only one of the two genes involved in translocation. In contrast to fusion-signal FISH, normal cells exhibit the yellow color in the split-signal FISH, whereas a translocation will result in a separate green and red signal.