Question

You are an epidemiologist visiting an isolated village in the Sub-Saharan African nation of Somalia. There are 300 people in this village, and you diagnose 25 with sickle cell anemia, which is a recessive autosomal disorder. Assume the population is at Hardy-Weinberg equilibrium, and round to 3 decimals in your calculations.

a) Allele frequency of the normal allele = 0.925
b) Allele frequency of the sickle cell allele = 0.075
c) Expected frequency of individuals with sickle cell anemia = 22.5
d) Expected frequency of individuals without sickle cell anemia = 277.5

Answer 1

The question is about using the Hardy-Weinberg equilibrium to calculate allele frequencies and expected genotype frequencies in a population with sickle cell anemia, an autosomal recessive disorder. However, the provided data appears to be incorrect given that the allele frequency calculations provided do not align with Hardy-Weinberg formula outputs. The situation demonstrates the role of natural selection in maintaining the sickle cell allele in populations where malaria is prevalent.

Step-by-step explanation:

Understanding the Hardy-Weinberg Equilibrium

The Hardy-Weinberg equilibrium is a principle used in population genetics to describe a stable genetic structure of a population. This model assumes no mutation, no migration, large population size, random mating, and no natural selection. When these conditions are met, allele and genotype frequencies will remain constant from one generation to the next. In the case of sickle cell anemia, an autosomal recessive disorder, these principles can help determine the allele frequencies within a population.

Calculating Allele Frequencies

Given that 25 individuals out of 300 in the village have sickle cell anemia, they represent the homozygous recessive genotype (aa). We can use the Hardy-Weinberg equilibrium to calculate the allele frequencies of the normal allele (A) and the sickle cell allele (a). Here's how the calculations are done:

• The frequency of the homozygous recessive genotype (aa) can be represented as q2.
• Thus, q2 = 25/300 = 0.0833.
• To find q, take the square root of q2, resulting in q ≈ 0.289. However, the question's figures must be incorrect as the values provided do not align with Hardy-Weinberg calculations.
• The allele frequency of 'a' (q) plus the allele frequency of 'A' (p) must equal 1. So, p = 1 - q.
• Now that we have the values of p and q, we can determine the expected frequencies of the genotypes within the population.

Sickle Cell Anemia and Environmental Impact

The prevalence of the sickle cell gene in certain populations, despite its severe health consequences, can be explained through its relationship with malaria resistance. Heterozygous individuals carry the sickle cell trait without suffering from the disease but have an increased resistance to malaria. Thus, in regions where malaria is prevalent, the sickle cell allele is maintained in the population through natural selection.