The Genetics of Sickle Cell Anemia
I. What is Sickle Cell Anemia?
A gene is a segment of DNA that codes for a protein or a trait. Genes can
be any length and sometimes involve multiple sections of DNA. The HBB
gene provides instructions for making a protein called Beta-globin which is
part of a large protein called hemoglobin that is found in red blood cells.
Each hemoglobin protein can carry four molecules of oxygen, which is
delivered to the body's organs and tissues. If a person doesn't have enough
red blood cells or the cells don't work properly, organs can become deprived
of oxygen. This condition is called anemia. A person with anemia may feel
tired all the time, experience difficulty with breathing, leg cramps, and
There is one type of anemia that is related to the shape of the HBB protein.
When a person has sickle cell anemia, the hemoglobin protein forms long
chains that change the shape of the red blood cell. Instead of a disc shaped
structure that moves easily through blood vessels, sickled blood cells are
shaped like bananas. The reason they have a sickled shape is because the
underlying gene has the wrong instructions. These misshapen blood cells
get clogged in vessels and don't have the life expectancy of normal blood
cells. A person with sickle cell disease will experience fatigue (feeling tired) and have episodes of extreme
pain, called a pain crisis. Sickled blood cells that block vessels in the brain can even cause stroke.
Sickle cell anemia is a life threatening disease that affects about 100,000 Americans. It is an inherited disease
that is passed from parents to their children, but parents can be carriers of the gene and not have any
symptoms. If both parents are carriers, their children have a 25% chance of having sickle cell anemia.
1. What is a gene? _____________________________________________________________
2. What is hemoglobin? _____________________________________________________________
3. How is a sickled blood cell different from a normal one? _______________________________________
4. Why are the blood cells the wrong shape? _________________________________________________
5. What are the symptoms of sickle cell anemia? ________________________________________________
6. What is a carrier? ________________________________________________
II. How DNA Makes Protein
Recall that DNA contains four bases: Adenine, Guanine,
Cytosine, and Thymine. The sequence of A's, T's, G's, and
C's are what determines...