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Practice Problems 1 1. Which of the following pieces of evidence disproved the hypothesis that life can arise spontaneously from a non-living system? Briefly explain your reasoning. A. B. C. D. E. The Miller and Urey experiment Louis Pasteur’s experiments boiling media in gooseneck flasks Discovery of organic molecules such as amino acids and sugars in samples from meteors Francesco Redi’s experiments putting meat into jars Polymerization of nucleotides on clay surfaces 2. What are two pieces of evidence to support the hypothesis that a likely progression from prebiotic chemistry to life on earth involved an “RNA world”? 3. How did the early “proto-cells” found in the RNA world differ from those that exist today? 4. Distinguish between the process by which membrane-bound organelles such as lysosomes and the nucleus formed, and the process by which mitochondria and chloroplasts arose. 5*. The following statement refers to one of the foundational experiments in origin-of-life research. The Miller-Urey experiment was flawed, and so chemical evolution in an abiotic environment is an implausible explanation for how life originated. A. B. Briefly explain the evidence that supports this statement. Briefly explain the evidence that this statement is an oversimplification, and that in fact chemical evolution may provide a plausible explanation for the origin of life. 6. Next-generation sequencing reveals six new mutations have occurred in the coding regions of genes in an individual diploid fly. If the coding regions of this fly comprise 100 million nucleotides per haploid genome, what is the mutation rate per nucleotide? 7. In a hypothetical population of gazelles, 28 individuals are homozygous for the d2 allele, 72 individuals are heterozygous for the d2 allele, and 100 individuals lack the d2 allele. What are the frequencies of the d1 and d2 alleles? 8. In a hypothetical population of sawflies, 20 percent of the population is homozygous for allele A and 45 percent is homozygous for allele a. Assuming that A and a are the only alleles at this locus, what percent of the population is heterozygous? 9. Indicate if you would expect Hardy-Weinberg equlibrium to be evident under the following conditions: Random mating Founder population No migration Inbreeding 10*. There are two isolated populations (“A” and “B”) of an endangered plant species. Population A has had a constant size of 2,000 plants and population B has had a constant size of 250 plants. A. We most expect to see the most significant increase in the frequency of deleterious alleles in population _____ due to _____. At a particular locus, two alleles are possible: M and m. In population A, the frequency of the M allele is 0.3. If Hardy-Weinberg equilibrium is in effect, what is the frequency of the m allele in this population? What is the expected frequency of the MM, Mm, and mm genotypes in this population? In population B, the frequency of the M allele is 0.8 and the frequency of the m allele is 0.2. What are two possible explanations for this difference in allele frequencies between the two populations? Which of the following would you expect to cause the most rapid change in the frequencies of the m and M alleles in population B? Briefly explain your reasoning. • Regular migration of individuals between population A and population B. • Mutation of the M allele into the m allele. • Mutation of the m allele into the M allele. • Nonrandom mating. B. C. D. E. 11. A. B. 12. A. B. C. Suppose that in a population of diploid organisms, a certain gene has only two alleles and mating is random (with respect to this gene, at least). Draw a graph showing how the frequency of heterozygotes in the population would vary depending on the frequency of the alleles in the population, assuming Hardy–Weinberg equilibrium. Hint: On the y-axis, plot the frequencies of heterozygotes as the frequency of one allele (on the x-axis) increases from 0 to 1 in intervals of 0.1 (0, 0.1, 0.2, etc.). At what allele frequency is the proportion of heterozygotes at a maximum? What is the frequency of heterozygotes at this frequency? A population of mice has been monitored for change over several generations. Following are five different bones and the changes to their means and extent of variation: Tibia: Mean increased 0.14 units, variation decreased Femur: Mean increased 0.08 units, variation increased Ulna: Mean did not change, variation increased Clavicle: Mean did not change, variation decreased Radius: Mean decreased 0.12 units, variation decreased Which is most likely to be under stabilizing selection? Which is most likely to be under disruptive selection? Which is most likely to be under directional selection to be smaller? 13. Refer to the graph below showing beak size for a population of a species of Darwin’s finches. A. Draw a graph showing what the resulting population would most likely look like after a generation of stronger stabilizing selection. Draw a graph showing what the resulting population would most likely look like after a generation of directional selection for smaller beak size. Draw a graph showing what the resulting population would most likely look like after a generation of strong disruptive selection. B. C. 14. Below is a table of the results of a study of grasshoppers showing frequencies of different size classes, along with the average number of offspring these individuals produce. Assuming that size is a heritable trait, what type of selection is operating in this population? Size (cm) 2.5−0.9 3.0−3.4 3.5−3.9 4.0−4.4 4.5−5.0 Frequency 0.19 0.26 0.28 0.21 0.06 Offspring 37 29 24 19 7 15. Fill in the blanks to complete the hypotheses depicted by the tree below. A. B. C. D. Humans share their most recent common ancestor with mice at node ____ Lizards share their most recent common ancestor with humans at node ____ Frogs share their most recent common ancestor with lizards at node ____ Fish share their most recent common ancestor with humans at node ____ 16. Which of the four trees in each of the following sets depicts a different pattern of relationships than the others? Set A: Set B: 17. Which of the following is an accurate statement of the relationships depicted in the tree on the right? A. Crocodile is more closely related to a lizard than crocodile to a bird. Crocodile is more closely related to a bird than crocodile to a lizard. Crocodile is equally related to lizard and bird Crocodile is related to a lizard, but is not related to a bird. B. C. D. 18*. Use the diagram below to answer the questions that follow. A. Which of the three phylogenetic trees of the Drosophila species is different from the other two? B. Based on Tree 1, indicate if the following statements are true or false. If false, correct the statement to make it true. D. simulans is more closely related to D. melanogaster than it is to D. pseudobscura. D. pseudobscura is more closely related to D. melanogaster than to D. sechella. D. melanogaster is an ancestor of D. sechella. 19. Two species of crickets have partially overlapping ranges. Hybrids are never found in the areas where the species meet. Individuals taken either from areas where they meet or areas where they do not meet will rarely mate in the lab because the females reject the songs sung by males of the other species. Of the few hybrids that are produced in lab crosses, all have low viability. What type of reproductive isolation so these crickets exhibit? 20. A. B. 21*. A. B. C. D. E. F. You decide to conduct a mark-recapture experiment to estimate the population size of mosquitofish in a small pond near your home. In the first catch, you mark 45 individuals. Two weeks later, you catch 62 individuals, of which 8 were marked. What is the estimated size of the population based on these data? What is one factor that could cause your estimate to be flawed? Predict the pattern in which each of the following species would most likely be distributed in space: Fiddler crabs, each of which defends its territory from other fiddler crabs. Ragweed seeds, which disperse by wind and grow where they land. Coconuts, which float in the ocean from one island to another. Sunflowers, which grow faster when not overcrowded. Ants, which live in colonies. For D and E, identify one specific factor for each that could cause it to adopt the strategy that it does. 22. The graphs below show the age distributions of male and female humans in Rwanda, Australia, Germany, and the United States. A. If conditions remain stable, which country is likely to experience the greatest growth in population over the next fifty years? If conditions remain stable, which country is likely to experience the greatest decrease in population over the next fifty years? B. 23*. A. You are studying a population of salamanders in a local pond. In a starting population of 400 salamanders, there are 80 new salamanders hatched and 40 salamanders that die in the span of one month. What is the size of the population at the end of the month during which you tracked it? B. C. D. E. What is the per capita birth rate for these salamanders per month? What is the per capita death rate for these salamanders per month? What is the per capita growth rate for these salamanders per month? If the per capita growth rate remains the same, how many salamanders would you expect to find if you return one month later? 24. For a long time, the Great Lakes in the United States supported large populations of many freshwater mussel species. Between 1960 and 2000, the populations of many of these species experienced a significant drop in size. What are two factors that could have contributed to this decline? 25. The African Black Rhinoceros is a large herbivore that is native to eastern and central Africa. Would you expect these rhinoceroses to exhibit the characteristics of an r-selected or a kselected species? What are two other characteristics that you would expect these rhinoceroses to exhibit, based on this selective regime? A. B. 26. A. B. C. D. E. F. G. H. I. 27. Characterize each of the following interactions as commensalism, parasitism, herbivory, mutualism (trophic, defensive, or dispersive, if applicable), predation, exploitation competition, interference competition, or amensalism. The relationship between flowering plants and the caterpillars that eat them. Orchids, a type of plant, require tree limbs for support but do not harm the trees. Oxpeckers, birds that ride on the backs of grazing mammals, have long been thought to provide benefits to African mammal hosts because they remove and feed on ticks (a parasite that embeds itself into the skin of the grazers). An experimental study in 2000 suggested that the oxpeckers actually drink the blood from the mammals and result in wounds that heal less quickly than if the tick were simply removed. In this type of relationship, the most common result is the death of one of the two interacting organisms. At some water bird breeding colonies, the large quantities of excrement from the birds may result in the death of vegetation underneath the trees in which their nests are built. The birds received no benefit or harm from the damage caused to the plants. Evidence suggests that some grasses benefit from being grazed. Termites live on cellulose, mostly derived from the dead wood they chew. They depend on protozoa in the gut to provide the enzymes that allow digestion of the wood. The protozoa would die outside of the termite, and the termite would starve without the protozoa to aid in digestion. Two species of birds feed on similar types of insects and nest in the same type of tree. Some plants contain compounds that, when mixed with the saliva of particular caterpillars species, creates an odor that attracts parasitoid wasps. Unlike true parasites, parasitoids like these wasps kill their hosts. The parasitoid wasps kill the caterpillars, often laying their eggs within their carcasses. This system is an example of _______ between the plant and the wasp, and the parasitoid could be considered a _______. Identify the strategy or strategies that each of the following species has used in the evolutionary arms race. A. B. C. D. E. 28. A. B. C. D. The Geometridae caterpillar avoids detection by predators while eating leaves by nibbling a pattern similar to the leaf’s own patterning, matching the leaf in color, and being shaped like a leaf spine The anglerfish is an example of a predator that uses both _______ and _______ to help catch its prey. Blending into its dark background, it waggles its head that has a fleshy, shimmering protuberance resembling a worm, which unsuspecting fish find irresistible. In trying to eat the fake worm, the fish finds itself the one being eaten. The distinctly recognizable black-and-white markings of a skunk, which can squirt foulsmelling spray onto a would-be predator. Coral snakes are brightly striped neotropical species whose fangs are venomous, dispensing a neurotoxin into their prey. The bright and distinctive color pattern on the snake, consisting of red, yellow, and black stripes, also acts as a warning to would-be predators. Another snake that is not venomous benefits from closely resembling the coral snake in terms of its coloration. Many species of bees and wasps have similar coloration, typically yellow and black. All species benefit from being recognized as potential stingers. Determine if each of the following traits illustrates coevolution. Some bats use sonar to detect and catch their prey. Some moth species preyed on by bats have evolved sensitivity to the bats’ high-pitched call sounds. Trait to consider: moth sensitivity to sounds Cheetahs are the fastest known land animal, but can only maintain their maximum speed for short periods of time. The gazelles on which they prey are thus sometimes able to escape predation. Trait to consider: cheetah’s inability to maintain their speed for long Some bats use sonar to detect and catch their prey. Some species of moth have evolved the behavior of diving down to avoid being caught. Bats, in turn, have evolved the strategy of catching moths over water because the moths get stuck on the water surface if they try to dive away. Trait to consider: bats hunting over water The Old World Swallowtail caterpillar feeds on the Fringed Rue plant. The plant produces certain oils that deter herbivores, but the caterpillar has evolved an insensitivity to these oils. Trait: Caterpillar’s insensitivity to oils.