Advanced Placement (AP) Biology Practice Exam

Which of the following best describes sickle cell disease?

1. Autosomal recessive disorder with normal hemoglobin

2. Autosomal dominant disorder leading to lung issues

3. Autosomal recessive disorder with mutated hemoglobin

4. Condition caused by environmental factors affecting red blood cells

The correct answer is: Autosomal recessive disorder with mutated hemoglobin

Sickle cell disease is accurately characterized as an autosomal recessive disorder with mutated hemoglobin. This condition arises from a mutation in the HBB gene, which encodes the beta-globin subunit of hemoglobin. The mutation leads to the production of an abnormal form of hemoglobin known as hemoglobin S (HbS). When the oxygen levels in the blood are low, HbS can cause red blood cells to become rigid and shaped like a sickle or crescent, which can impede blood flow and lead to various health complications. In individuals who are carriers of one normal allele and one mutated allele, they are referred to as having sickle cell trait, which typically does not present with symptoms. However, those who inherit two copies of the mutated gene (one from each parent) develop sickle cell disease, exhibiting a range of symptoms including pain episodes, anemia, and increased susceptibility to infections. This understanding emphasizes the genetic basis of the disease rather than suggesting any environmental or dominant inheritance factors, which are not accurate in this context.