Which condition is characterized by a macrocytic, normochromic anemia?

Pernicious anemia is characterized by macrocytic, normochromic anemia due to a deficiency in vitamin B12, which is essential for DNA synthesis in red blood cell production. When there is inadequate vitamin B12, the red blood cells produced are larger than normal (macrocytic) and tend to retain normal color due to adequate hemoglobin content (normochromic). This type of anemia often results from an autoimmune destruction of cells in the stomach that produce intrinsic factor, necessary for vitamin B12 absorption.

In contrast, the other conditions mentioned do not present with macrocytic normochromic anemia. Iron deficiency anemia typically results in microcytic, hypochromic red blood cells due to insufficient iron levels. Thalassemia is a genetic disorder leading to microcytic anemia as well, related to hemoglobin production deficits. Hemolytic anemia is characterized by the premature destruction of red blood cells, leading to a different set of morphological changes depending on the underlying cause but does not typically lead to macrocytosis. Thus, pernicious anemia is the only condition among the choices that presents with the specific characteristics of macrocytic, normochromic anemia.