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Genetic / Evolution Results

The blood disease beta-thalassemia results from homozygosity for a defective allele in the gene coding for the beta hemoglobin subunit. Homozygotes for the beta-thalassemia allel die in childhood, while heterozygotes appear normal. This disease is common in the region around the Mediterranean sea, including the island of Sardinia, where malaria was prevalent until recently. You visit this island in order to examine the frequency of the allele in people who have lived there for thousands of years.

a) You find that the frequency of children born with the disease in the population is 0.01. What is the frequency of heterozygotes for the allele? What assumption must you make to arrive at your answer?

b) If heterozygotes for the beta-thalassemia allele are protected against malaria, what is the selection coefficient s1 aganist homozygotes for the normal allele? Again, what assumption must you make in your calculation?

c) Because of spraying and other public health meausres over the last few decades, malaria is no longer a public health problem on Sardinia. What should happen to the frequency of the beta-thalassemia allele in the Sardinia population in the future? What type of selection will bring about this change?

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This question is about Hardy-Weinberg equilibrium and the dynamics of alleles for the disease β-thalassemia in a population which has historically been exposed to a particularly strong selective force for the disease allele, namely the presence of another disease, malaria. The Hardy-Weinberg theory of population genetics gives a means of predicting allele frequencies in populations which are randomly breeding and theoretically closed, ie. there is no immigration or emigration, mutation, or selection acting on the alleles of interest. Since this question specifically relates to a situation where there is selection, the population is not in Hardy-Weinberg equilibrium. There is a pretty good summary of the main concepts of this theory here if you need to review them:

All the same, the equilibrium gives us a place to start, from which we can account for any deviations from the above assumptions.

The main idea behind the theory is that an equilibrium exists such that genotype frequencies are constant from generation to generation when the ...

Solution Summary

The expert examines genetic evolution and results. A blood disease for beta-thalassemia results are determined.