EBK CAMPBELL BIOLOGY
EBK CAMPBELL BIOLOGY
10th Edition
ISBN: 9780136539414
Author: Reece
Publisher: VST
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Chapter 1.4, Problem 2CC

MAKE CONNECTIONS Ø The gene that causes sickle-cell disease is present in a higher percentage of residents of sub-Saharan Africa than among those of African descent living in the United States. Even though this gene causes sickle-cell disease, it also provides some protection from malaria, a serious disease that is widespread in sub-Saharan Africa but absent in the United States. Discuss an evolutionary process that could account for the different percentages of the sickle-cell gene among residents of the two regions. (See Concept 1.2.)

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Steven Frank and Laurence Hurst argued that a cytoplasmically inherited mutation in humans that has severe effects in males but no effect in females will not be eliminated from a population by natural selection because only females pass on mtDNA (S. A. Frank and L. D. Hurst. 1996. Nature 383:224). Using this argument, explain why males with Leber hereditary optic neuropathy are more severely affected than females.
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 generation
Recall from our classes on molecular evolution that some proteins evolve more rapidly than others. For example, the oxygen-carrying protein myoglobin evolves more quickly than the D1 protein of photosystem II.  What explains this difference in the rate of protein evolution?  A. Proteins like myoglobin have evolved more recently than proteins like D1 and thus have been forced to evolve more quickly. B. Changes to the sequence of some proteins can be tolerated as they don’t alter fitness; for other proteins, sequence changes are usually harmful. C. In constrained proteins like D1, evolution results primarily from nucleotide changes that alter the amino acid sequence of the protein.  D. Protein evolution is dependent upon the rate of gene mutation and some genes have a higher rate of mutation than others.
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