What does the southern blotting technique detect?

• A. Specific RNA molecules in a sample
• B. Protein sequences in cells
• C. Specific DNA sequences in DNA samples
• D. Metabolites in biological fluids

Answer: (C)

Southern blotting is a molecular biology technique specifically designed to detect specific DNA sequences within a complex mixture of DNA. This method involves several key steps: first, DNA is extracted from the sample and then digested using restriction enzymes, which cut the DNA into smaller fragments. These fragments are then separated based on size through gel electrophoresis, where they migrate through a gel matrix. After electrophoresis, the DNA is transferred from the gel onto a membrane, typically made of nylon or nitrocellulose.

Once the DNA is on the membrane, a labeled DNA probe—complementary to the specific sequence of interest—binds to its target sequence on the membrane. This probe is typically labeled with a radioactive or fluorescent tag that allows for visualization. After hybridization, excess probe is washed away, and the areas where the probe has bound can be detected, indicating the presence of the specific DNA sequence.

This technique is fundamental in various applications, including gene mapping, forensic analysis, and detecting gene mutations, making it a powerful tool for genetic analysis. In contrast, the other techniques listed, such as those focused on RNA detection (often referred to as Northern blotting), protein detection (Western blotting), or metabolite analysis (different biochemical assays),