What is the function of the second probe in the FISH technique?

The second probe in the FISH (Fluorescence In Situ Hybridization) technique serves as a critical component for internal control of chromosome number. The main function of this additional probe is to help verify that the number of chromosomes being analyzed is correct, ensuring that the sample contains the proper number of chromosomes expected. This control is essential in distinguishing between true abnormalities and artifacts that may arise during the preparation of the fluorescent signals.

Using a second probe that targets a specific region or marker allows for precise identification of the target chromosomes and confirms the results obtained from the primary probe. This dual-probe approach enhances the reliability of the analysis, particularly in complex samples where chromosome number and structure may vary, as it helps ensure that any changes detected are genuinely indicative of the underlying biology rather than errors in the measurement process.