27. Which of the following statements best explains the prevalence and geographic distribution of sickle cell anemia allele (HbS).   The homozygotes for normal hemoglobin protein are always at an advantage in all environments.   Homozygous recessive individuals are selected for in malarial environments.   Heterozygous individuals are at a selective advantage in malarial environments.   Sickle cell anemia is found in high frequencies only among West Africans and their descendants.   none of the above.

What is the heterozygous advantage of people having sickle-cell trait in areas where malaria is a major cause of death?

4. In a region of Africa, where malaria is prevalent, 40% of the population are found to have sickle-cell anemia. The disease is caused by an abnormal hemoglobin that is found in both homozygotes (S2S2) and heterozygotes (S1S2). Many homozygotes (S2S2) suffer from anemia and often die. Heterozygotes (S1S2) incur a much less debilitating malady called "sickling trait". Approximately 3% of the people with abnormal hemoglobin are homozygotes (1.2\% of the entire population). The fitness of the S2S2 homozygotes is only 1/4 that of the heterozygotes. Where malaria is prevalent, heterozygotes exhibit overdominance with respect to fitness. If we assume that the above population is at an equilibrium frequency for the allele causing sickle-cell anemia (S2), calculate the relative fitness of the S1S1 homozygotes (which have normal hemoglobin).

Below is a pedigree for a family into which Individual III-4 has married. He and his spouse, Individual III-3, are visiting a genetic counselor because they are expecting a baby (Individual IV-1). They want to know the chance that the baby will get the autosomal recessive genetic disease seen in Individual II-2. Overall, in the population, the disease is known to affect 1 in 625 individuals in the population to which this family belongs [assume this frequency is the result of random mating so represents f(aa)] I. II. E III. IV. 1 1 2 2 3 1 3 1 4 2 4 5

2

Is the heritability of human skin color in a particualr city greater in the summer? Please explain why

Sickle cell anemia is a genetic disease most common in those of African ancestry that results from the mutation of a single basepair. This mutation results in a change to the hemoglobin protein. In this experiment, “S” will represent the normal allele and “s” thesickle allele. They are codominant alleles. Therefore, SS is normal, Ss is not fatal but mildly symptomatic, and ss is debilitating,painful, and often fatal. After hundreds or even thousands of generations, both alleles are still common in those of African ancestry. How would you explain this?

9. (4) Sickle cell anemia is an autosomal recessive disorder. If the frequency of sickle cell anemia in Hispanic Americans is 1 in 16,300 and the population is mating randomly for the sickle cell gene, what proportion of the Hispanic American population consists of heterozygous carriers of the CF allele?