**Core Concept**
Southern blotting is a laboratory technique used to detect specific DNA sequences in a sample. It involves the separation of DNA fragments by size using gel electrophoresis, followed by their transfer to a membrane and hybridization with a labeled probe.

**Why the Correct Answer is Right**
Southern blotting is specifically designed for detecting DNA sequences, which makes it a powerful tool for genetic analysis. The process involves the denaturation of DNA, followed by its separation by size using gel electrophoresis. The separated DNA fragments are then transferred to a membrane, typically nylon or nitrocellulose, and hybridized with a labeled probe that is complementary to the target DNA sequence. The labeled probe binds to the target DNA sequence, allowing for its detection.

**Why Each Wrong Option is Incorrect**
**Option A:** Western blotting is a technique used for detecting proteins, not DNA sequences.
**Option B:** Northern blotting is used for detecting RNA sequences, not DNA sequences.
**Option C:** PCR (Polymerase Chain Reaction) is a technique used for amplifying DNA sequences, but it is not a blotting technique.

**Clinical Pearl / High-Yield Fact**
Southern blotting is a crucial technique in molecular biology, allowing researchers to detect specific DNA sequences in a sample. It is often used in genetic research, forensic analysis, and diagnostic testing.

**Correct Answer: D. Southern blotting is used for detecting DNA sequences.**