Question

sickle cell: natural selection in humans
film activity student handout

1. there are two alleles, or variations, of the gene that encodes the subunit of hemoglobin relevant to sickle cell disease: the mutated sickle cell allele (s) and the unmutated allele (s). a person homozygous for the sickle cell allele (ss) has sickle cell disease. a person with a heterozygous genotype (ss) has sickle cell trait. individuals with sickle cell trait:

a. might develop sickle cell disease later in life
b. tend to have many sickle - shaped red blood cells
c. usually have no symptoms of sickle cell disease

1. to determine an individuals hemoglobin genotype, dr. allison collected a blood sample, placed the sample on a slide, and then:

a. looked for the presence of malaria parasites within the red blood cells
b. ran a series of genetic tests to detect sickle cell alleles in blood cells
c. added a chemical to create a low - oxygen environment to see if it affected red blood cells

1. when researching sickle cell disease, dr. allison discovered that the frequency of the sickle cell trait in kenya was higher in humid lowlands than in the drier highlands. he hypothesized that the differences in the frequency of the sickle cell trait in these regions were due to:

a. the presence of many more malaria - carrying mosquitoes in the lowlands than in the highlands
b. less available medical care to treat malaria in the lowlands compared to the highlands
c. higher rates of individuals infected with sickle cell trait in the lowlands than in the highlands

1. dr. allison claimed that being heterozygous for the sickle cell allele provides a selective advantage against malaria. which of the following provides evidence supporting this claim?

a. more children under five years of age died of malaria than individuals over five years of age.
b. a higher percentage of children had the sickle cell trait and malaria in the drier highlands than in the humid lowlands.
c. children without the sickle cell trait had higher malaria parasite counts in their blood than those with sickle cell trait.

1. one potential mechanism for why heterozygous individuals are protected from severe malaria infections is because the malaria parasites:

a. cannot easily digest hemoglobin when red blood cells become sickled
b. cannot freely circulate when sickled cells stick to blood vessels
c. have to more actively compete for food because they reproduce too quickly in sickled red blood cells

Explanation:

1. Heterozygous (Ss) individuals have sickle - cell trait and usually no symptoms of sickle - cell disease.
2. To determine hemoglobin genotype, a chemical was added to create a low - oxygen environment to see if it affected red blood cells as sickle - shaped cells form under low - oxygen conditions.
3. Higher frequency of sickle - cell trait in humid lowlands is hypothesized to be due to more malaria - carrying mosquitoes in lowlands.
4. Evidence that heterozygous for sickle - cell allele provides advantage against malaria is that children without the trait had higher malaria parasite counts.
5. One mechanism for protection in heterozygous individuals is that malaria parasites cannot easily digest hemoglobin when red blood cells sickle.

Answer:

1. c. usually have no symptoms of sickle cell disease
2. c. added a chemical to create a low - oxygen environment to see if it affected red blood cells
3. a. the presence of many more malaria - carrying mosquitoes in the lowlands than in the highlands
4. c. Children without the sickle cell trait had higher malaria parasite counts in their blood than those with sickle cell trait.
5. a. cannot easily digest hemoglobin when red blood cells become sickled