What are DNA probes commonly used for?

DNA probes are commonly used to detect specific DNA sequences, making this option the correct choice. A DNA probe is a fragment of DNA or RNA that is labeled with a detectable marker, such as a fluorescent dye or radioactive isotope. When introduced into a sample, these probes will hybridize, or bind, to complementary sequences of DNA present in the sample. This hybridization process allows researchers and scientists to identify the presence of certain genetic material, which can be crucial for various applications, including genetic testing, diagnosing diseases, and conducting forensic analysis.

In contrast, the other options involve different biological processes or tools. Measuring protein levels typically employs techniques like ELISA or Western blotting, rather than DNA probes. Sequencing RNA involves methods that focus on nucleic acid sequences directly rather than using probes designed for DNA. Modifying gene expression often requires gene editing techniques or regulatory elements rather than the detection capabilities that probes provide. Thus, DNA probes serve a unique and vital role in the identification of specific DNA sequences within various samples.