In FISH, what is the key feature of a painting probe?

A painting probe is specifically designed to cover all or part of a chromosome, allowing researchers to visualize the entire chromosome structure or a large segment of it during fluorescence in situ hybridization (FISH) analysis. This broad coverage is crucial in applications where it's important to assess chromosome integrity, identify structural abnormalities, or analyze chromosomal rearrangements. By labeling regions of the chromosome with fluorescent dyes, a painting probe can provide a comprehensive view that facilitates the identification of chromosomal anomalies within the context of the entire genome.

In contrast, the other choices represent different functions that probes can have but do not capture the essence of what a painting probe does. For instance, while some probes do focus on identifying specific genes, painting probes serve a much broader purpose. Similarly, while internal controls are important in validating the results of any assay, this is not the primary role of painting probes. Lastly, hybrid capture techniques involve different methodologies and are not directly related to the defining function of painting probes in FISH.