midterm1.5.test

Bio 1M03 Version 5 1. Xenopus tropicalis and Xenopus laevis are two closely related species of frog. X. laevis has two times the number of chromosomes as X. tropicalis. X. laevis most likely arose through: A. allopatric speciation B. polyploidy C. reinforcement D. coevolution 2. Disruptive selection at the trait level is most likely to cause what kind of selection at the allele level? A. Balancing selection B. Stabilizing selection C. Negative selection on rare alleles D. Directional selection 3. Stabilizing selection at the trait level is often associated with A. Positive selection on rare alleles B. Negative selection on rare alleles C. Frequency-dependent selection D. Genetic drift 4. Yeasts grown in unstable environments develop the ability to quickly shut down their metabolism and survive in a resting state for long periods of time. The ability is itself an . The fact that the yeast can develop the ability is probably due to . A. adaptation; adaptation B. adaptation; acclimation C. acclimation; adaptation D. acclimation; acclimation 5. E. coli bacteria grown for many generations in the lab with limited food sources developed the ability to use glucose as a food source. Their ancestors did not have this ability, and neither did control strains grown under similar conditions with ample food. These experiments provide evidence that: A. Evolution can occur in the laboratory B. Natural selection can occur in the laboratory C. Bacteria can evolve the ability to use glucose for food D. All of the above Page 2

Bio 1M03 Version 5 6. When we say an allele is “fixed” in a population, it means: A. It is the most fit allele for that locus under current conditions B. A defect in that allele has been repaired C. It is the only allele present at that locus in the population D. The allele is not subject to mutation 7. A species of frog was separated into two populations in the Andean mountains several thousand years ago by a cold spell that prevented them from living on hills separating two valleys. Offspring from the two populations are now observed to survive, grow and reproduce well on the hills and in the valleys. These two populations are most likely undergoing A. Fusion B. Divergence through reinforcement C. Speciation through hybridization D. Competitive exclusion E. Allopolyploidy Use the following information for the next two questions. Researchers raised 10 lines of bacteria starting from genetically identical individuals. After 100 generations, bacteria in 7 of these lines developed the ability to use one of the starches on the laboratory dishes as a new food sources. Subsequent experiments showed that these bacteria could out-compete ancestral strains, and the bacteria from the other three lines, under the laboratory conditions. 8. What is the most likely explanation for the observed change in the 7 lines? A. Random mutation B. Genetic drift C. Natural selection D. Random mutation combined with natural selection E. Genetic drift combined with natural selection 9. What is the most likely explanation for why the other 3 lines did not show the same change? A. The laboratory conditions were different for these lines B. These lines were subject to sexual selection C. These lines had a different set of random mutations D. These lines were subject to more gene flow Page 3

Bio 1M03 Version 5 14. A population of maize plants has a recessive allele at a locus with simple dominance that heritably causes them to grow extra tall. The population genotype frequencies are near the Hardy-Weinberg expectation. A windstorm kills all of the extra tall plants, but not others. If we measure the population after the windstorm, we expect to find: A. genotype frequencies are near the new Hardy-Weinberg expectation (based on the new allele frequencies) B. more heterozygotes than the expectation C. more homozygotes than the expectation D. more tall alleles than the expectation E. more short alleles than the expectation 15. The biological species concept does not apply at all to A. strictly asexual populations B. extinct populations C. populations with many different “morphotypes” that all look different from each other D. populations that can survive in a wide variety of habitats and conditions 16. Which of the following definition best reflects an advantage in evolutionary fitness? A. Organisms that tend to live longer B. Organisms that are better at competing for resources C. Organisms that tend to have more success at finding mates D. Organisms that tend to produce more viable offspring 17. All madrigals can sublimate. Alice is a madrigal. Bob can sublimate. Which of the following must be true? A. Alice can sublimate B. Bob is a madrigal C. Both D. Neither 18. All cows can fly. Dushoff can fly. Therefore, Dushoff is a cow. What is wrong with this logic (assuming we accept the assumptions)? A. nothing; the logic is correct B. The first assumption would need to say “Only cows can fly” C. The order of the assumptions would need to be reversed D. The two assumptions contradict each other Page 5

Bio 1M03 Version 5 19. Two populations of bugs live on two different species of trees in the same forest. The adult bugs breed together sometimes, but the hybrid offspring are rarely able to survive to adulthood, because they are not well adapted to either species of tree. This is an example of isolation that will likely lead to . A. pre-zygotic; fusion B. post-zygotic; fusion C. pre-zygotic; natural selection for post-zygotic isolation D. post-zygotic; natural selection for pre-zygotic isolation Use this information for the next three questions. At a certain allele, humans with the genotype NN are vulnerable to tuberculosis, those with the genotype CN have normal lung function and not vulnerable to tuberculosis, and those with genotype CC don’t have normal lung function. 20. This is an example of A. polyploidy B. inbreeding C. simple dominance D. complex dominance 21. In an environment with high rates of tuberculosis, the genotype CN has the highest fitness. This is an example of A. directional selection B. balancing selection C. disruptive selection D. negative selection on allele N E. positive selection on allele N 22. In an environment with low rates of tuberculosis, the genotype NN has the highest fitness. This is an example of A. directional selection B. balancing selection C. disruptive selection D. negative selection on allele N E. positive selection on allele N Page 6

Bio 1M03 Version 5 27. What is the genotype frequency of heterozygotes? A. 0.25 B. 0.4 C. 0.45 D. 0.55 E. 0.65 28. What is the expected phenotype frequency of plants with white flowers? A. 0.25 B. 0.4 C. 0.45 D. 0.55 E. 0.65 29. A biologist is trying to classify ancient, extinct, shellfish into species based on the shapes of their shells, with no genetic information. They are most likely to use which applicable species concept? A. Biological B. Morphological C. Ecological D. Phylogenetic 30. Two populations of pine trees live in the same area, but open their flowers at different times, so that they rarely mate with each other. If a scientist argues that this fact makes them different species, which species concept are they applying? A. Biological B. Morphological C. Ecological D. Phylogenetic Page 8

Bio 1M03 Student # Version 5 Short-answer questions Answer questions in pen . Briefly show necessary work and equations. Points may be deducted for wrong information, even when the correct information is also there. 31. Researchers in the 1700s did an experiment designed to understand the origin of microbes. They placed nutrient broth in two jars. One was sealed completely, and one was covered with cheese cloth that was meant to allow air to move in and out. They found that microbes grew in the cloth-covered jar, but not the sealed jar. a) (2 point) What is a major problem with the experiment as described? What two principles can be applied to improve the experiment? Give a brief explanation of how you would do this. b) (2 points) Assume the researchers redid the experiment and found a similar result to the first experiment. What can you conclude? What remains uncertain (from the perspective of 18th century researchers who would have tried this experiment)? 32. A population of maize plants has a locus with two alleles: E is associated with early flowering (and thus early breeding) and L is associated with late flowering. You observe 70 plants that flower early, 40 that flower late, and 50 that flower in between. a) (2 points) Assume that these observations are driven only by the locus under study. What is your estimate of the genotype frequencies in this population? Page 9