**Core Concept**
Beta-thalassemia minor is a genetic disorder characterized by a mutation in the HBB gene, leading to reduced production of the beta-globin chains of hemoglobin. This results in a mild anemia with a normal or near-normal red blood cell count but with a significant reduction in the production of the beta-globin chains.

**Why the Correct Answer is Right**
The main abnormality in beta-thalassemia minor is the reduced production of the beta-globin chains, which is due to a mutation in the HBB gene that affects the transcription of the beta-globin gene. This mutation leads to a decrease in the production of the beta-globin chains, resulting in a decreased production of hemoglobin A (HbA) and an increased production of hemoglobin A2 (HbA2) and hemoglobin F (HbF). The reduced production of beta-globin chains is the primary abnormality in beta-thalassemia minor.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not specify the genetic basis of beta-thalassemia minor.
**Option B:** This option is incorrect because it does not accurately describe the primary abnormality in beta-thalassemia minor.
**Option C:** This option is incorrect because it is a characteristic of beta-thalassemia major, not beta-thalassemia minor.

**Clinical Pearl / High-Yield Fact**
Beta-thalassemia minor is often referred to as a "silent carrier" because it may not present with any significant clinical symptoms, but it can still be transmitted to offspring.

**Correct Answer: D. Reduced production of beta-globin chains.**