**Core Concept**
FISH (Fluorescence In Situ Hybridization) is a molecular cytogenetic technique used to detect and locate specific DNA sequences on chromosomes. It involves the use of fluorescent probes that bind to specific DNA sequences, allowing for the visualization of the targeted region.

**Why the Correct Answer is Right**
FISH is widely used in various applications, including the detection of gene amplifications, deletions, and translocations. It is particularly useful in the diagnosis of genetic disorders, such as Down syndrome, and in the identification of cancer-specific genetic alterations. FISH can also be used to detect microdeletions and microduplications, which are associated with various genetic syndromes. The technique is highly sensitive and specific, allowing for the detection of specific DNA sequences in interphase cells.

**Why Each Wrong Option is Incorrect**
**Option A:** FISH is not primarily used for protein expression analysis, which is typically performed using immunohistochemistry or Western blotting.
**Option B:** While FISH can be used to detect gene expression, it is not the primary technique used for this purpose, as techniques like RT-PCR and RNA FISH are more commonly used.
**Option C:** FISH is not typically used for DNA sequencing, as this is usually performed using next-generation sequencing technologies.

**Clinical Pearl / High-Yield Fact**
FISH is a highly sensitive and specific technique that can be used to detect specific DNA sequences in interphase cells, making it a valuable tool in the diagnosis of genetic disorders and cancer.

**Correct Answer:** A. FISH is used for the detection of gene amplifications, deletions, and translocations.