**Core Concept**
Dubin Johnson syndrome is a rare genetic disorder characterized by chronic jaundice due to an inability to secrete conjugated bilirubin into the bile. The underlying defect lies in the gene encoding a protein responsible for the transport of conjugated bilirubin and other organic anions from hepatocytes into the bile canaliculi.

**Why the Correct Answer is Right**
The defective gene in Dubin Johnson syndrome encodes the ATP-binding cassette C2 (ABCC2) protein, also known as the multidrug resistance-associated protein 2 (MRP2). ABCC2 is a member of the ATP-binding cassette (ABC) transporter family and plays a crucial role in the efflux of conjugated bilirubin and other organic anions from hepatocytes into the bile. The mutation in the ABCC2 gene disrupts the normal functioning of MRP2, leading to the accumulation of conjugated bilirubin in the bloodstream, resulting in jaundice.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because the gene encoding the ATP-binding cassette C1 (ABCC1) protein is associated with another disorder, not Dubin Johnson syndrome.
* **Option B:** This option is incorrect because the gene encoding the multidrug resistance protein 1 (MRP1) is not directly related to the pathogenesis of Dubin Johnson syndrome.
* **Option C:** This option is incorrect because the gene encoding the cytochrome P450 3A4 (CYP3A4) enzyme is involved in the metabolism of various drugs, not the transport of conjugated bilirubin.

**Clinical Pearl / High-Yield Fact**
Dubin Johnson syndrome is characterized by a unique "bronzey" discoloration of the skin and sclerae due to the accumulation of melanin-like pigment, in addition to chronic jaundice.

**Correct Answer: C. ABCC2 (MRP2)**