Question

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Sickle-cell disease is an autosomal recessive disorder that causes the red blood cells of an affected person to be rigid and abnormally shaped. The life expectancy of a person affected by the disorder is approximately 45 years. Carriers of the disease produce some sickled cells, but not enough to be symptomatic.


Malaria is a potentially fatal disease caused by the protist Plasmodium falciparum.


Studies have shown that those affected by sickle-cell disease (genotype ss), as well as carriers who possess only one sickle-cell allele (Ss), are much more resistant to malaria than those with homozygous dominant genotypes (SS). This resistance is created in part by the rupturing of any sickled red blood cells that are infected with the parasite, preventing Plasmodium falciparum from reproducing and making it more susceptible to the host's immune system.


Which of the following statements best predicts what would happen in response to a prolonged epidemic of malaria in a population with no previous exposure to malaria?


A. The frequency of the homozygous recessive genotype (ss) would decrease.

B. The frequency of the dominant allele (S) would increase.

C. The frequency of the sickle-cell allele (s) would increase.

D. The frequency of the homozygous dominant genotype (SS) would increase.

Answer 1

Step-by-step explanation:

Sickle cell disease is a group of disorders that affects hemoglobin, the molecule in red blood cells that delivers oxygen to cells throughout the body. People with this disorder have atypical hemoglobin molecules called hemoglobin S, which can distort red blood cells into a sickle, or crescent, shape.

Signs and symptoms of sickle cell disease usually begin in early childhood. Characteristic features of this disorder include a low number of red blood cells (anemia), repeated infections, and periodic episodes of pain. The severity of symptoms varies from person to person. Some people have mild symptoms, while others are frequently hospitalized for more serious complications.

The signs and symptoms of sickle cell disease are caused by the sickling of red blood cells. When red blood cells sickle, they break down prematurely, which can lead to anemia. Anemia can cause shortness of breath, fatigue, and delayed growth and development in children.

Answer:

D. The frequency of the homozygous dominant genotype (SS) would increase.

Answer 2

Answer: the correct answer is C. The frequency of the sickle-cell allele 9s) would increase.

Step-by-step explanation: