Question

what is a major cause of microcytosis?

Explanation:

Microcytosis (small red blood cells) is most commonly caused by iron deficiency. Iron is essential for hemoglobin synthesis; without enough iron, red blood cells can't form properly and become smaller (microcytic). Other causes like thalassemia exist, but iron deficiency is a major, widespread cause.

Answer:

Iron deficiency (a major cause of microcytosis is iron deficiency, as insufficient iron hinders hemoglobin production, leading to smaller red blood cells)