Name: ________________________________________ Block: ______________ Date: ______________
Sickle Cell Disease & Malaria Resistance
Sickled = curved
or crescent shaped;
shaped like a sickle
(curved blade)
Erythrocyte = fancy
science word for Red
Blood Cell (RBC)
Sickled erythrocytes are found intermixed with normal erythrocytes in the blood of people with both
sickle cell disease and sickle cell trait. Image courtesy of the National Institute of Health's Heart, Lung,
and Blood Institute.
http://www.nlm.nih.gov/medlineplus/sicklecellanemia.html
Nucleobase =
sequence of
nucleotide
bases (the A’s,
T’s, C’s, & G’s
of DNA)
Anemia = A
disease where
you do not have
enough red
blood cells to
carry sufficient
oxygen to your
body’s organs
Autosomal = any numbered
chromosome that is not a sex
chromosome (X,Y)
Sickle cell disease, or sickle cell anemia is an autosomal recessive disease caused by
hemoglobin S, an oxygen-carrying protein in blood cells. A single point mutation in the
nucleobase sequence of chromosome 11 causes the sixth amino acid in the
hemoglobin protein, glutamic acid, to be replaced by valine, changing standard
hemoglobin beta into hemoglobin S.[2] The sickle shape is caused by hemoglobin’s
resulting structural change, and it is from this structure that the disease gets its name. [1]
People with either HbAS (heterozygous with hemoglobin A and hemoglobin S) or HbSS
(homozygous with hemoglobin S) are considered to have sickle cell trait and can show
symptoms of sickle cell disease. However, when an individual is homozygous recessive
for hemoglobin S, severe symptoms start to occur. The most infamous being anemia,
which can, in turn, cause shortness of breath, jaundice, and high blood pressure. This
biggest problem is blood clotting in vessels, which could lead to damaged tissues that
rely on the clotted vessels. Individuals heterozygous for the trait are not prone to the
same severity of symptoms as homozygous recessive individuals.[1]
Despite the disease’s lethal symptoms, it protects the carrier from malaria, which is
why sickle cell alleles are most common in people of African descent (about 7% of
people of African descent carry an allele), and other areas where malaria is
prevalent.[3] Sickle cell trait is hypothesized to have evolved because of the vital
protection from malaria it provides.[9] Furthermore, individuals with HbAS tend to
Carrier = A person
survive better than individuals with HbSS as they are not exposed to the same
who only has one
severity of risks yet still receive protection from malaria.
Lethal =
deadly
allele for the trait
(heterozygous)
Name: ________________________________________ Block: ______________ Date: ______________
Directions: Answer the questions below in at least one paragraph (> 5 sentences).
1) How does sickle cell disease relate to malaria resistance?
2) If you could choose, which genotype for the hemoglobin gene would you want? Why?
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