Chapter 13

Summarize the key points of Darwin's theory of descent with modification, including his proposed mechanism of evolution.

Which of the following did not influence Darwin as he synthesized the theory of evolution by natural selection? a. examples of artificial selection that produce large and relatively rapid changes in domesticated species b. Lyell's Principles of Geology, on gradual geologic changes c. comparisons of fossils with living organisms d. Mendel's paper describing the laws of inheritance

Natural selection is sometimes described as "survival of the fittest." Which of the following best measures an organism's fitmess? a. how many fertile offspring it produces b. how strong it is when pitted against others of its species C. its ability to withstand environmental extremes d. how much food it is able to make or obtain

In an area of erratic rainfall, a biologist found that grass plants with alleles for curled leaves reproduced better in dry years, and plants with alleles for flat leaves reproduced better in wet years. This situation would tend to \(\quad\) (Explain your answer.) a. cause genetic drift in the grass population. b. preserve genetic variation in the grass population. c. lead to stabilizing selection in the grass population. d. lead to uniformity in the grass population.

If an allele is recessive and lethal in homozygotes before they reproduce, a. the allele will be removed from the population by natural selection in approximately 1,000 years. b. the allele will likely remain in the population at a low frequency because it cannot be selected against in heterozygotes. c. the fitness of the homozygous recessive genotype is \(0 .\) d. both \(b\) and \(c\) are correct.

In a population with two alleles, \(B\) and \(b\), the allele frequency of \(b\) is \(0.4 . B\) is dominant to \(b\). What is the frequency of individuals with the dominant phenotype if the population is in Hardy-Weinberg equilibrium? a. 0.16 b. 0.36 c. 0.48 d. 0.84

Within a few weeks of treatment with the drug \(3 \mathrm{TC}\), a patient's HIV population consists entirely of 3TC-resistant viruses. How can this result best be explained? a. HIV can change its surface proteins and resist vaccines. b. The patient must have become reinfected with a resistant virus. c. A few drug-resistant viruses were present at the start of treatment, and natural selection increased their frequency. d. HIV began making drug-resistant versions of its enzymes in response to the drug.

In the late 1700 s, machines that could blast through rock to build roads and railways were invented, exposing deep layers of rocks. How would you expect this development to aid the science of paleontology?

In the early 1800 s, French naturalist Jean Baptiste Lamarck suggested that the best explanation for the relationship of fossils to current organisms is that life evolves. He proposed that by using or not using its body parts, an individual may change its traits and then pass those changes on to its offspring. He suggested, for instance, that the ancestors of the giraffe had lengthened their necks by stretching higher and higher into the trees to reach leaves. Evaluate Lamarck's hypotheses from the perspective of present-day scientific knowledge.

Sickle-cell disease is caused by a recessive allele. Roughly one out of every 400 African Americans \((0.25 \%)\) is afflicted with sickle-cell disease. Use the Hardy-Weinberg equation to calculate the percentage of African Americans who are carriers of the sickle-cell allele. (Hint: \(\left.q^{2}=0.0025 .\right)\)

It seems logical that natural selection would work toward genetic uniformity; the genotypes that are most fit produce the most offspring, increasing the frequency of adaptive alleles and eliminating less adaptive alleles. Yet there remains a great deal of genetic variation within populations. Describe factors that contribute to this variation.

Cetaceans are fully aquatic mammals that evolved from terrestrial ancestors. Gather information about the respiratory system of cetaceans and describe how it illustrates the statement made in Module 13.18 that "Evolution is limited by historical constraints."

A population of snails is preyed on by birds that break the snails open on rocks, eat the soft bodies, and leave the shells. The snails occur in both striped and unstriped forms. In one area, researchers counted both live snails and broken shells. Their data are summarized below: $$ \begin{array}{|lcccc|} \hline & & & \underline{\phantom{xxx}} \\ & \text { Striped } & \text { Unstriped } & \text { Total } & \text { Percent Striped } \\ \text { Living } & 264 & 296 & 560 & 47.1 \\ \text { Broken } & 486 & 377 & 863 & 56.3 \\ \hline \end{array} $$ Which snail form seems better adapted to this environment? Why? Predict how the frequencies of striped and unstriped snails might change in the future.

Advocates of "scientific creationism" and "intelligent design" lobby school districts for such things as a ban on teaching evolution, equal time in science classes to teach alternative versions of the origin and history of life, or disclaimers in textbooks stating that evolution is "just a theory." They argue that it is only fair to let students evaluate both evolution and the idea that all species were created by God as the Bible relates or that, because organisms are so complex and well adapted, they must have been created by an intelligent designer. Do you think that alternative views of evolution should be taught in science courses? Why or why not?