Life: The Science of Biology
11th Edition
ISBN: 9781319010164
Author: David E. Sadava, David M. Hillis, H. Craig Heller, Sally D. Hacker
Publisher: W. H. Freeman
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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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- What is heterozygote superiority ? There's a link between evolution of sickle cell trait and malaria. Comment.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_forwardWhat 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_forward
- The 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_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_forwardThe above data are from a landmark student looking into the relationship between sickle cell anemia and malaria. These data are from a population where malaria is prevalent. A is the allele for normal red blood cells; S is the sickle cell allele (you should know what this means). Is this population in H-W equilibrium? Make sure to use chi-square. Why or why not (if not, what assumption(s) violated). Genotype AA AS SS Total Observed 9365 (75.6%) 2993 (24.2%) 29 (0.2%) 12,387arrow_forwardWhat impact might a vaccine against malaria have on the frequency of the Sickle Cell allele in Africa in the long run?arrow_forward
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