Life: The Science of Biology
11th Edition
ISBN: 9781319010164
Author: David E. Sadava, David M. Hillis, H. Craig Heller, Sally D. Hacker
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Chapter 20.5, Problem 1R
Summary Introduction
To review:
A hypothesis to explain that a deleterious allele, like sickle-cell anemia, could become fixed in a population.
Introduction:
Sickle-cell anemia is a genetic disease, which occurs in individuals, who are homozygous recessive for an allele that affects the hemoglobin gene. There is a strong negative selection against this allele, but it is quite common in central Africa, particularly in areas where malaria was highly prevalent historically.
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If 9% of an African population is born with a severe form of sickle-cell anemia (ss), what percentage of the population will be more resistant to malaria because they are heterozygous (Ss) for the sickle-cell gene?
Explain the High frequency of the sickle-cell allele HbβS in regions of Africa where malaria is prevalent?
What is heterozygote superiority ? There's a link between evolution of sickle cell trait and malaria. Comment.
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Life: The Science of Biology
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- Tristan da Cunha is a group of small islands in themiddle of the Atlantic Ocean. In 1814, a group of 15British colonists founded a settlement on these islands.In 1885, 15 of the 19 males on the island were lost ina shipwreck. In the late 1960s, four cases of retinitispigmentosa, which progressively leads to blindness,were found among the 240 descendants of these settlers remaining on the island. The frequency of retinitis pigmentosa in Britain is about 1 in 6000. Explainthe high incidence of this disease on Tristan daCunha relative to that seen in Britain.arrow_forwardAn allele of the G6PD gene acts in a recessive manner to cause sensitivity to fava beans, resulting in ahemolytic reaction (lysis of red blood cells) afteringestion of the beans. The same allele also confersdominant resistance to malaria. The heterozygote hasan advantage in a region where malaria is prevalent.Will the equilibrium frequency (qe) be the same foran African and a North American country? Whatfactors affect qe?arrow_forwardDo you think the allele for sickle cell anemia would be common in regions where malaria did not exist? Explain why or why not.arrow_forward
- In parts of equatorial Africa, where the malaria parasite is most common, the sickle-cell allele constitutes 20% of the ß-hemoglobin alleles in the human gene pool. The sickle cell trait provides an advantage against malaria compared to people with normal hemoglobin. In the United States, the parasite that causes malaria is not present, but African Americans whose ancestors were from equatorial Africa have the sickle-cell B- hemoglobin allele. These differences in traits illustrate O inclusive fitness because people have evolved molecular differences to adapt to environmental stimuli O inclusive fitness because ß-hemoglobin increases the proliferation of beneficial traits in the population O relative fitness because people have evolved molecular differences to an environmental pathogen O relative fitness because the molecular differences in ß-hemoglobin are passed to the next generationarrow_forwardAbout 9 percent of Caucasian males are color-blind andcannot distinguish red-colored from green-coloredobjects.a. Offer one genetic model for color blindness.b. Explain why and how color blindness has reached afrequency of 9 percent in this populationarrow_forwardThe prevalence (frequency) of sickle-cell disease in Canada is quite low, affecting 1/3800 individuals. However, in some African populations 1/25 individuals are affected by sickle-cell disease. The difference in frequency of this allele within the differing populations has to do with the adaptation pressures that exist in the different environments. Individuals with the heterozygous genotype have a survival advantage in environments where the disease malaria is prevalent as the presence of this mutant allele leads to resistance to malaria. Therefore, the sickle-cell disease tends to be more frequent in environments where the malaria parasite is most common. Question: Explain why the sickle-cell disease remains frequent in some populations while it exists in very low frequency in other populations.arrow_forward
- What would happen to the frequency of heterozygous carriers of sickle-cell anemia (with AS genotype) if mosquitoes were completely wiped out in a large region?arrow_forwardDescribe the effect of malaria on the frequency of the HbS allele in areas where malaria is common:In areas with malaria, which individual would survive better and leave more offspring- an individual with two HbA alleles or an individual with one HbA allele and one HbS allele? Given this, would you expect the HbS allele to be common or rare in populations living with malaria?arrow_forwardHumans who are born homozygous for the recessive sickle cell allele die of sickle cell anemia, while those who are heterozygous are resistant to malaria. 5% of the population of the Congo are homozygous recessive for the sickle cell allele. What percentage of the population is resistant to malaria?arrow_forward
- If the genotype AA is susceptible to malaria but with no sickling, the genotype AS is resistant to malaria with mild sickling, and the genotype SS is resistant to malaria but has severe sickling and anemia, the individual living in an environment with malaria with the best chance of survival is a person with genotype _.arrow_forwardWhat impact might a vaccine against malaria have on the frequency of the Sickle Cell allele in Africa in the long run?arrow_forwardEntomologists at the New York State Department of Agriculture are interested in determiningthe connection between pest insects infesting crop plants with populations of the same insectinfesting native plants in natural habitats. Long term trapping and monitoring studies haveestimated that on average 3% of the populations move between habitats (farm to natural and visversa) each generation. A new insecticide resistance allele (∆K) has begun to increase infrequency in the agricultural populations. A genotyping survey at this locus of 50 individuals ineach population has revealed the following genotype counts: K/K K/∆K ∆K/∆K Agricultural field 32 16 2 Forest 48 2 0 4a. Based on the effects of migration alone, what will the frequency of ∆K be in the forestpopulation in the next generation? 4b. If migration was acting in here without selection, what would the frequency of ΔK be in theagricultural population in the next generation? 4c. If the natural forest population was…arrow_forward
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