Practice Problems 1 Answer Key 1. Louis Pasteur and Francesco Redi performed experiments disproving spontaneous generation – Redi of animals, and Pasteur of microorganisms. The other experimental results provide support for the idea that chemical evolution is possible, and that organic molecules may have arisen spontaneously (or been transported to Earth from elsewhere in the universe), but did not disprove the possibility of spontaneous generation. 2. Several answers are possible; some include • Its ability to replicate by base-pairing • Its significance in gene expression • Its ability to act as both genetic material and a catalyst • The use of RNA to initiate DNA synthesis (primase uses RNA nucleotides) • “Vestigial” ribonucleotides in other biological molecules 3. There are many differences; some include • They had fatty acid membranes, rather than phospholipid membranes. • They had RNA, not DNA, genomes • They relied on basic chemical and physical properties to grow and divide rather than regulated growth and division 4. The ER, lysosomes, and the nucleus formed when the plasma membrane invaginated and pinched off to form internal compartments within prokaryotic cells. In contrast, mitochondria and chloroplasts arose when free-living bacteria were engulfed by eukaryotic cells, and incorporated as subcellular structures rather than broken down. Over time, genes from the mitochondria and chloroplast genomes were transferred to the genome of the cell, though these structures maintain their own genomes to this day. 5A. The Miller-Urey experiment did not include all of the gasses that were present on the early earth. In addition to those gasses included in the Miller-Urey experiment, volcanic eruptions would have released H2S and SO2 into the atmosphere. In addition, Miller and Urey were able to detect amino acids and other organic molecules, but not nucleic acids. When these additional gasses were included in follow-up experiments, additional organic molecules including nucleotides and lipids were produced. In other words, using “more accurate” approximations of the early earth’s atmosphere, researchers were able to produce more of the molecules of life than had previously been possible. B. 6. 100 million nucleotides per haploid genome corresponds to 200 million nucleotides per diploid genome. If six coding-sequence mutations were detected, that is 6 mutations per 200 million nucleotides, or 3 per million nucleotides, or 1 per 33,333,333 nucleotides. This is 0.00000003 (3 x 10-8) mutations per nucleotide. 7. F (d1) = (2x 100 + 72)/400 = 0.68 F (d2) = (2 x 28 + 72)/400 = 0.32 8. 100 – (20 + 45) = 35 9. Random mating YES Founder population NO No migration YES Inbreeding NO 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. B. B; genetic drift The applicability of HWE is irrelevant; if there only two alleles, and the frequency of one of them is 0.3, the frequency of the other is 0.7. Thus the frequency of the m allele is 0.7. F(MM) = 0.32 = 0.09 F(Mm) = 2 x 0.3 x 0.7 = 0.42 F(mm) = 0.72 = 0.49 A number of explanations are possible; some include • Genetic drift has randomly caused differences in allele frequencies • The populations may be under different selective pressures so that the M allele is more favorable/advantageous in population B • Population B may have arisen from a founder population with a higher frequency of the M allele • Population A may have arisen from a founder population with a higher frequency of the m allele Regular migration of individuals between the populations would cause the most rapid change in the frequencies of the m and M alleles in population B. Mutations occur very slowly, and are unlikely to change allele frequencies significantly in the absence of an additional factor such as selection. Nonrandom mating changes genotype frequencies, but not allele frequencies, unless there is another contributing factor, such as selection. C. D. E. 11A. B. The frequency of heterozygotes is maximized when allele frequencies are equal, 0.5 each. At this allele frequency, 2pq = 2 x 0.5 x 0.5 = 0.5 12A. B. C. Clavicle Ulna Radius 13A. B. C. 14. Directional selection for smaller individuals 15A. B. C. D. 1 2 3 4 16. Set A: c is different from the others. Set B: a is different from the others 17. B 18A. B. Tree 3 is different from the others. D. simulans is more closely related to D. melanogaster than it is to D. pseudobscura. TRUE D. pseudobscura is more closely related to D. melanogaster than to D. sechella. FALSE – D. pseudoobscura is equally closely related to D. melanogaster and D. sechella. D. melanogaster is an ancestor of D. sechella. FALSE – D. melanogaster shares a common ancestor with D. sechella. 19. Prezygotic: behavioral Postzygotic: low hybrid viability 20A. B. • 349 Possible answers include An decreased likelihood for marked fish to survive (for example due to increased susceptibility to predation) Differences in the probability of initial capture vs. re-capture Differences in trap efficacy during the two days, so that the proportion of the population captures is not constant • • 21A. B. C. D. E. F. Regular Random Random Regular Clumped Some possible answers for each are: • The sunflowers may benefit from regular spacing because it provides them with more access to sunlight, or water, or nutrients in the soil. • Ants may choose their colony locations based on the availability of food or suitability of location for building the next. Ant colonies are like small cities, with different groups of ants playing different roles, so that the ants rely on each other for survival and would not likely persist in a random or regular dispersion pattern. 22A. Rwanda B. Germany 23A. B. C. D. E. 440 80/400 = 0.2 40/400 = 0.1 0.2 – 0.1 = 0.1 The population would increase by 440 x 0.1 = 44 salamanders, for a final population size of 484 after a second month. 24. A number of explanations are possible, including Overfishing by humans Increase in other predators Reduction in food availability Introduction of a competitor (this actually played a huge role – search for Great Lakes + zebra mussels for more information) Pollution affecting fertility and/or survival • • • • • 25A. B. • • • • • k-selected You would expect them to also: Exhibit slow development Have a relatively low reproductive rate Have a relatively late reproductive age Live a long time Etc. 26A. B. C. D. E. F. Herbivory Commensalism The birds prey on the ticks, and are parasites of the grazing animals Predation Amensalism Mutualism (without knowing more about the benefit to the grasses, it is difficult to say for sure what type of mutualism it is.) Mutualism (without knowing more about the benefit to the protozoa, it is difficult to say for sure what type of mutualism it is.) Exploitation competition Defensive mutualism (the wasps kill the caterpillar, protecting the plant, in exchange for the benefit of easier location of caterpillars); predator G. H. I. 27A. B. C. D. E. Crypsis/cryptic coloration Crypsis/cryptic coloration; aggressive mimicry Aposematic coloration The coral snake exhibits aposematism, the other snake exhibits Batesian mimicry Mullerian mimicry and aposematic coloration 28A. B. C. D. Yes No Yes Yes
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