What potential impact can hemoglobin D have on red blood cell characteristics?

Hemoglobin D is a variant form of hemoglobin that can influence red blood cell characteristics significantly. When hemoglobin D is present, particularly in cases like Hemoglobin D disease or when it is combined with other hemoglobinopathies (such as beta-thalassemia), it can lead to a condition where the red blood cell production is compromised. This often results in a decrease in both the size, which may lead to microcytic red blood cells, and the number of red blood cells.

In certain circumstances, individuals with hemoglobin D can develop mild anemia, which is characterized by having fewer than normal red blood cells. The presence of abnormal hemoglobin can disrupt normal erythropoiesis (the production of red blood cells), which can further contribute to this decrease. Therefore, the impact of hemoglobin D on red blood cell characteristics aligns with the decrease in both size and number, leading to the answer being correct.