**Core Concept**
Microcytosis refers to a condition characterized by the presence of small red blood cells (erythrocytes) in the peripheral blood smear. This condition can be caused by various factors, including iron deficiency anemia, thalassemia, and chronic diseases.

**Why the Correct Answer is Right**
Microcytosis is often seen in iron deficiency anemia due to the reduced availability of iron for hemoglobin synthesis. This leads to the production of smaller, more fragile red blood cells. In iron deficiency anemia, the body's demand for iron exceeds its supply, resulting in the impaired synthesis of heme, a critical component of hemoglobin. The erythropoietic system compensates by producing smaller red blood cells, leading to microcytosis.

**Why Each Wrong Option is Incorrect**
* **Option A:** While anemia of chronic disease can cause normocytic anemia, it is not typically associated with microcytosis.
* **Option B:** Sickle cell anemia is characterized by abnormally shaped (sickle-shaped) red blood cells, not microcytosis.
* **Option C:** Polycythemia vera is a condition characterized by an overproduction of red blood cells, leading to macrocytosis, not microcytosis.

**Clinical Pearl / High-Yield Fact**
Iron deficiency anemia is the most common cause of microcytosis and can be diagnosed using serum ferritin levels, which reflect the body's iron stores.

**Correct Answer: B. Sickle cell anemia is characterized by abnormally shaped (sickle-shaped) red blood cells, not microcytosis.