**Core Concept**
The infant's condition is characterized by spherocytosis, anemia, jaundice, and splenomegaly, indicating a defect in the production or maintenance of red blood cells, specifically affecting their shape and resulting in premature destruction in the spleen.

**Why the Correct Answer is Right**
The infant's condition is most likely caused by a genetic mutation affecting the spectrin protein, which is crucial for maintaining the structural integrity of red blood cells. Spectrin is composed of two subunits, alpha and beta, and mutations in either of these subunits can lead to hereditary spherocytosis (HS). The elevated reticulocyte count suggests a compensatory response to the anemia, indicating that the bone marrow is producing more red blood cells to replace those being destroyed.

**Why Each Wrong Option is Incorrect**
* **Option A:** Defective ankyrin protein is associated with a different type of spherocytosis, known as hereditary spherocytosis with ankyrin deficiency.
* **Option B:** Defective band 3 protein is associated with hereditary spherocytosis with band 3 deficiency, but it is not the primary cause in this case.
* **Option D:** Defective protein 4.2 is associated with a rare form of hereditary spherocytosis, but it is not the most common cause of this condition.

**Clinical Pearl / High-Yield Fact**
Hereditary spherocytosis is an autosomal dominant disorder, meaning that a single copy of the mutated gene is sufficient to cause the condition, and it affects approximately 1 in 2,000 individuals of European descent.

**Correct Answer:** C.