Some individuals have a specific mutation in the primary sequence of their hemoglobin molecules that causes them to aggregate, resulting in a deformation of their red blood cells. This abnormality is genetic in nature. A person may inherit the gene from one parent and have sickle cell trait (only some of the hemoglobin is hemoglobin S), which is usually not life-threatening. Inheriting the gene from both parents will result in sickle cell disease, which is a very serious condition.
Context:
Two sisters went to the hospital. The medics ran some blood tests and found out that Sue had sickle cell trait, while Mary had normal blood cells. Sue received treatment.
Q: Which sister has hemoglobin molecules that aggregate?