Final answer:
The hemoglobin variant common in Southeast Asia that migrates with hemoglobin C at pH 8.6 is hemoglobin E (HbE), known for its role as a genetic adaptation against malaria.
Step-by-step explanation:
The hemoglobin variant that is commonly seen in the Southeast Asian population and migrates with hemoglobin C (HbC) at pH 8.6 is known as hemoglobin E (HbE). This variant is the result of a mutation in the beta chain of hemoglobin, leading to the formation of an abnormal hemoglobin variant. Hemoglobin E is particularly prevalent in regions where malaria is or has been endemic, and it acts as a genetic adaptation against the disease. Unlike the other hemoglobins mentioned, such as hemoglobin Bart's, which is associated with alpha-thalassemia, and hemoglobin H (HbH), which also involves an abnormal alpha chain, hemoglobin E carries a mutation that provides some protective effect against malaria similar to hemoglobin S (HbS) and hemoglobin C (HbC).