**Core Concept**
Interphase Fluorescence In Situ Hybridization (FISH) is a molecular cytogenetic technique used to detect and locate specific DNA sequences on chromosomes. This method involves the hybridization of fluorescently labeled probes to the target DNA sequences, allowing for the visualization of the specific genetic material under a fluorescence microscope.

**Why the Correct Answer is Right**
FISH is primarily used for the detection of genetic abnormalities, such as chromosomal translocations, deletions, and amplifications, which are commonly associated with various diseases, including cancer. The technique is particularly useful for identifying specific genetic markers, such as the BCR-ABL fusion gene in chronic myeloid leukemia (CML). FISH can also be employed for the detection of aneuploidy, which involves the presence of an abnormal number of chromosomes, and for the identification of microdeletions, which are small deletions of genetic material.

**Why Each Wrong Option is Incorrect**
**Option A:** FISH is not primarily used for the diagnosis of infectious diseases.
**Option B:** While FISH can be used for the detection of genetic mutations, it is not the preferred method for determining the genetic basis of complex diseases.
**Option C:** FISH is not typically used for the detection of protein expression levels.

**Clinical Pearl / High-Yield Fact**
FISH is a valuable tool in the diagnosis and management of hematological malignancies, and its results can have significant implications for patient treatment and prognosis.

**Correct Answer:** C.