The fitnesses of sickle-cell anemia genotypes in the presence of malaria have been calculated as follows: wAA = 0.9 (Homozygous for HbA allele) wAS = 1 (Heterozygous carrier) wSS = 0.2 (Homozygous for HbS allele) What is the selection coefficient (s) against the normal allele?
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In a population of the Yoruba ethnic group living in a region of Nigeria with a high prevalence of malarial infection, the frequency of the HbS allele for sickle-cell hemoglobin was 0.2. Suppose that individuals in this population mate randomly, and that the fitness of HbS/HbS homozygotes in this environment is only 15% as high as HbA/HbS heterozygotes. If the frequency of the HbS allele in this population represents an equilibrium involving malaria-induced selection against HbA/HbA homozygotes vs. selection against HbS/HbS homozygotes, then what is the estimated relative fitness of HbA/HbA homozygotes in this environment?
Sri K.
The gene for sickle-cell anemia exhibits heterozygote advantage (= overdominance). An individual who is an Hb-A/Hb-S heterozygote has increased resistance to malaria and therefore has greater fitness than the Hb-A/Hb-A homozygote, who is susceptible to malaria, and the Hb-S/Hb-S homozygote, who has sickle-cell anemia. Suppose the fitness values of the genotypes in Mozambique are presented here: Hb-A/Hb-A = 0.80 Hb-A/Hb-S = 1.00 Hb-S/Hb-S = 0.14 a. What will be the allele frequencies after one generation of selection starting with allele frequencies Hb-A = 0.9 and Hb-S = 0.1? b. What will be the allele frequencies after one generation of selection starting with allele frequencies Hb-A = 0.6 and Hb-S = 0.4? c. Given the fitness values above, what is the equilibrium frequency for Hb-A? Are your results from a and b consistent with that equilibrium frequency? Explain why or why not.
Adi S.
In a large, randomly mating population, the frequency of the allele for sickle-cell disease is 0.028. We are interested in the frequency of the sickle-cell allele in the next generation. Genotypes and the average number of offspring are listed below. What are the current genotype frequencies? Select all three genotypes: f(SS) = 0.945 f(Ss) = 0.972 f(ss) = 0.028 What are their fitness values? Select all three genotypes: WSS = 0.83 WSs = 0.83 Wss =
Katlin K.
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