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The Evolution of Populations

This chapter explores the concepts of genetic variation, allele frequencies, Hardy-Weinberg equilibrium, and the evolution of drug resistance. It also discusses the factors that drive the frequency of genetic diseases such as cystic fibrosis and the role of mutation, genetic drift, and selection in population evolution.

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The Evolution of Populations

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  1. Chapter 23 The Evolution of Populations Questions prepared by Jung Choi Georgia Institute of Technology Michael Dini Texas Tech University

  2. Genetic Variation The original source of all genetic variation is _____. • natural selection • sexual reproduction • independent assortment • recombination • mutation

  3. Evolution In evolutionary terms, an organism's fitness is measured by its _____. • stability in the face of environmental change • contribution to the gene pool of the next generation • genetic variability • mutation rate • health

  4. Allele Frequencies red = 0.36, white = 0.16 red = 0.6, white = 0.4 red = 0.5, white = 0.5 Allele frequencies cannot be determined unless the population is in equilibrium. Red short-horned cattle are homozygous for the red allele, white cattle are homozygous for the white allele, and roan cattle are heterozygotes. Population A consists of 36% red, 16% white, and 48% roan cattle. What are the allele frequencies?

  5. Hardy-Weinberg Equilibrium Determination A B both A and B neither A nor B Which of these populations are in Hardy-Weinberg equilibrium?

  6. Cystic Fibrosis 1 1/2,500, or about 0.04% 1/50, or about 2% 1/25, or about 4% The frequency cannot be calculated because selection violates Hardy-Weinberg assumptions. The frequency of cystic fibrosis, a recessive genetic disease, is 1 per 2,500 births among Northern Europeans. Assuming random mating, what is the frequency of carriers?

  7. Until the 1950s, infants born with cystic fibrosis did not survive longer than a few months. If the frequency of carriers was 4% in the year 1900, what proportion of CF alleles was eliminated in one generation? 100% 50% 4% 2% <0.1% Cystic Fibrosis 2

  8. The frequency of cystic fibrosis is extremely low among Asians and Africans. What may explain the relatively high frequency of cystic fibrosis among Northern Europeans? Cystic Fibrosis 3 • bottleneck effect • founder effect • genetic drift • directional selection • balancing selection

  9. Evolution of Drug Resistance in HIV, with Time after Initiation of Treatment Before treatment with 3TC, did 3TC-resistant viruses exist in these patients? • yes • no • no way to tell

  10. Mutation If 3TC resistance carries a cost, what will happen to the proportion of the drug-resistant virus after 3TC treatment stops? • It will increase. • It will decline. • It will stay the same. • It will drift randomly. • There is no way to predict what will happen.

  11. A high proportion of the cats on Key West have extra toes (polydactyly). What is the most likely explanation? • high rate of mutation • founder effect • bottleneck effect • directional selection for extra toes

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