Biology Study Material: Evolution and Natural Selection, Exams of Ecology and Environment

Download Biology Study Material: Evolution and Natural Selection and more Exams Ecology and Environment in PDF only on Docsity! BIOL 204, Fall 2008 Midterm 1, Form A Name__Short Answer Key___ 1 I. Multiple choice. (35 pts.) Select the best single answer from the choices given and fill in the appropriate bubble. 1) Climate scientists have extracted a record of global average temperature and atmospheric CO2 concentrations using gases trapped in ice cores, and these two correspond closely over the last several glacial/interglacial cycles, as shown in the figure above. These data A. conclusively show that elevated CO2 causes higher global temperatures B. conclusively show that higher global temperatures cause elevated atmospheric CO2 C. show that atmospheric CO2 concentrations and global temperatures are strongly correlated, but by themselves don’t allow us to determine which causes which. D. None of the above 2) Many crustaceans (e.g., lobsters, shrimp, and crayfish) use their tails to swim, but crabs have reduced tails that curl under their shells and are not used in swimming. This is an example of: A. artificial selection B. an extinction C. the law of succession D. a vestigial trait E. convergent evolution 3) Some beetles and flies (insects) have antler-like structures on their heads, much like male deer (chordates) do. The existence of antlers in beetle, fly, and deer species with strong male-male competition is an example of: A. structural homology B. developmental homology C. genetic homology D. analogy/convergent evolution 4) A farmer uses triazine herbicide to control pigweed in his field. For the first few years, the triazine works well and almost all the pigweed dies; but after several years, the farmer sees more and more pigweed. Which of these explanations best describes this observation? A. The herbicide company lost its triazine formula and started selling poor-quality triazine. B. Natural selection caused the pigweed to mutate, creating a new triazine-resistant species. C. Triazine-resistant pigweed has less efficient photosynthesis metabolism. D. Only triazine-resistant weeds survived and reproduced, so each year more pigweed was triazine-resistant. 5) If you can’t measure it repeatably and verifiably, A. it’s too small. B. it’s not worth thinking about. C. it’s not science. D. it must be love. E. it’s Howdy Doody time. 6) What do the nodes and branch points on a phylogenetic tree represent? A. species B. new kingdoms or domains C. ancestral groups that split into two descendant groups D. groups that got new names BIOL 204, Fall 2008 Midterm 1, Form A Name__Short Answer Key___ 2 7) A species of insect that commonly forages for food on the bark of shrubs has coloration that varies from brown to red. Birds feeding on this insect can find and eat the red-colored individuals more easily than the brown individuals. However, females of this species of insect prefer to mate with red-colored males, so that red males have more offspring than brown males if the red males survive to reproduce. A researcher observes that the percentage of different colored individuals remains stable in the study population from year to year. If the researcher prevents bird predation on the study population by putting nets over shrubs, what would you expect to happen to the distribution of colors in the population over time? A. The percentage of red individuals should increase over time. B. The percentage of brown individuals should increase over time. C. The distribution of colors should not change. D. Genetic drift should cause the coloration in the population to randomly fluctuate over time. 8) The preceding question is an example A. of balancing selection B. of sexual selection C. that shows that evolution may not lead to a single optimal phenotype D. all of the above 9) Vestigial traits and neutral changes in DNA sequences are good examples of: A. adaptation B. acclimation C. convergent traits D. nonadaptive traits E. developmental homology 10) How can Darwinian fitness be estimated? A. Document how long different individuals in a population survive. B. Count the number of offspring produced by different individuals in a population. C. Determine which individuals are strongest. D. Determine which phenotype is the most common one in a given population. 11) Why does the presence of extinct and transitional forms in the fossil record support the pattern component of the theory of evolution by natural selection? A. It supports the hypothesis that individuals change over time. B. It supports the hypothesis that weaker species are eliminated by natural selection. C. It supports the hypothesis that species evolve to become more complex and better adapted over time. D. It supports the hypothesis that species have changed through time. 12) Why are homologous traits similar? A. They are derived from a common ancestor. B. They are derived from different ancestors. C. They result from convergent evolution. D. They result from gene flow from adjacent populations. 13) What are the four requirements for evolution by natural selection in a given population? A. (1) The population varies; (2) all variation is heritable; (3) some individuals produce more offspring than others; (4) populations differ in their production of offspring. B. (1) Individuals in a population vary; (2) the variation is neutral; (3) offspring are produced that can survive; (4) individuals produce offspring. C. (1) Individuals in a population vary; (2) the variation is heritable; (3) more offspring are produced than can survive; (4) all individuals have different alleles. D. (1) Individuals in a population vary; (2) the variation is heritable; (3) some individuals produce more offspring than others; (4) certain traits lead to greater reproductive success than other traits. 14) Has evolution by natural selection recently occurred in populations of Mycobacterium tuberculosis? A. Yes; some people are now resistant to tuberculosis, but before they weren’t. The resistance alleles have changed frequency in some human populations. B. Yes; the frequency of the adaptive allele for drug resistance has increased over time. C. No; evolution has not occurred, because the resistance trait occurs with a frequency of approximately 10 percent. D. No; Mycobacterium tuberculosis is still the same species. BIOL 204, Fall 2008 Midterm 1, Form A Name__Short Answer Key___ 5 25) The data above show how soapberry bugs differ in beak length in two populations, those growing a mating on small fruited plants and those growing and mating on large seeded plants. Of the four evolutionary processes, which two are most important in causing this event even though populations occupy the same geographic area? A. mutation and selection B. genetic drift and mutation C. reduced gene flow and mutation D. reduced gene flow and genetic drift E. reduced gene flow and selection 26) The genes for the traits that Mendel worked with often are located on different chromosomes, or they are so far apart on the same chromosome that crossing over almost always occurs between them. How did this circumstance help Mendel recognize the principle of independent assortment? A. Otherwise, his dihybrid crosses would not have produced a 9:3:3:1 ratio of F2 phenotypes. B. The occurrence of individuals with unexpected phenotypes led him to the discovery of recombination. C. It led him to the realization that the behavior of chromosomes during meiosis explained his results. D. It meant that the alleles involved were either dominant or recessive, which gave 3:1 ratios in the F1 generation. 27) A large amount of gene flow is now occurring among human populations due to intermarriage among people from different ethnic groups and regions of the world. This phenomenon is A. increasing racial differences in our species B. decreasing racial differences in our species C. selecting for differences in skin color in our species D. raising the likelihood that reproductive barriers could arise among humans E. none of the above 28) What does it mean when an allele reaches fixation? A. It is eliminated from the population. B. It has a frequency of 1.0. C. It is dominant to all other alleles. D. It is adaptively advantageous. 29) Intelligent design provides testable alternative hypotheses to evolutionary theory. A. True B. False 30) Evolution cannot explain the presence of complex structures in organisms, such as eyes or flagella, that must operate as a unit. A. True B. False 31) While Darwin proposed natural selection as the mechanism of evolution, he didn’t know how heritability occurred. A. True B. False BIOL 204, Fall 2008 Midterm 1, Form A Name__Short Answer Key___ 6 32) Darwin conclusively showed that natural selection is the only mechanism by which evolution occurs. A. True B. False 33) Evolution favors the development of more complex organisms over simpler organisms. A. True B. False 34) A scientific concept, such as evolution, does not become a “theory” until it convincingly ties together a large number of independent observations and repeatable experiments. A. True B. False 35) Though dolphins evolved more recently than alligators, that doesn’t influence how well-adapted each type of species is to its environment. A. True B. False II. Short answer (35 points total). For questions involving calculations, you need to show all work and equations used, or you will not get full credit (even if you get the numerical answer correct). 1. (5 pts.) What is the best current definition of evolution? A change in allele frequencies in a population over time. 2. (6 pts.) Name at least 3 mechanisms that could cause microevolution, and state whether they necessarily increase fitness, decrease fitness or leave fitness unchanged. Natural selection – by definition increases fitness of population over time as less fit individuals are selected against. Note: this includes directional selection, disruptive selection, stabilizing selection, AND sexual selection. Yes, the last of these does increase fitness: while there may be a tradeoff with survival, overall the sexually selected individuals must still have higher reproductive fitness, otherwise their traits wouldn’t become more common in the population. Genetic drift – could increase fitness, decrease fitness, or leave fitness unchanged, depending on the random fluctuations of alleles frequencies. Bottleneck effects and founder effects are both subsets of genetic drift. Gene flow - could increase fitness, decrease fitness, or leave fitness unchanged, depending on which traits come with individuals into the population. Often, gene flow can slow selection to novel environments, but it can also provide adaptive alleles to populations lacking them. Mutation – formation of new alleles by changes in DNA. These changes could increase fitness, decrease fitness, or leave fitness unchanged. Note: while it’s true that most mutations are deleterious or neutral, there’s a very, very important exception: the occasional beneficial mutation. These are the ones that are the stuff of natural selection! Nonrandom mating - We’ve already covered sexual selection above, which increases fitness; inbreeding, the other main form of nonrandom mating we discussed, generally decreases fitness through the accumulation of deleterious recessive homozygotes. But if you just said non-random mating without specifying sexual selection or inbreeding, you’d have to say either increase or decrease fitness. 3) In humans, albinism is caused by loss-of-function mutations in genes involved in the synthesis of melanin, the dark pigment in skin. Albinism is an autosomal (not sex-linked) recessive trait. In Americans of northern European ancestry, albino individuals are present at a frequency of about 1 in 10,000 (or 0.0001). Show all work and equations used in the calculations below to get full credit. a) (2 pts). What is q, the frequency of the recessive allele in this population? The recessive homozygote genotype is present at a frequency of 0.0001, which is equivalent to q2 in the H-W equation: p2 + 2pq + q2 = 1. So q, the allele frequency of the recessive allele = square root(0.0001) = 0.01. BIOL 204, Fall 2008 Midterm 1, Form A Name__Short Answer Key___ 7 b) (4 pts) Assuming that the genes for albinism are in Hardy-Weinberg equilibrium, what is the frequency of “carriers” in this population? Carriers are those individuals that carry an allele for albinism, but don’t show the trait. p2 + 2pq + q2 = 1, and, p + q = 1. So, p = 1 - 0.01 = 0.99 2pq = frequency of heterozygote carrier genotype = 2(0.99)(0.01) = 0.0198 Note: I strongly recommend NOT switching back and forth between frequencies and percentages unless explicitly requested. It’s too easy to mix up decimal places! c) (4 pts.) A man and woman are both of normal pigmentation, but both have one parent who is albino (without melanin pigmentation). What is the probability that their first child will be an albino? Since both the man and woman have a homozygote recessive parent, they must have a recessive allele. Since neither is albino, they must be heterozygous. So, if A = normal melanin and a = lack thereof, then Aa x Aa gives a 1:2:1 genotype ratio of AA:Aa:aa, with aa as albino. The chance of the first child being albino is therefore ¼. A Punnett square can be useful here. 4. Gray seed color in peas is dominant to white. Assume that Mendel conducted a series of experiments where plants with gray seeds were crossed among themselves, and the following progeny were produced: 302 gray and 98 white. a) (3 pts.) What is the most probable genotype of each parent? (Assume the following symbols: G = gray and g = white.) A 3:1 ratio of dominant phenotype to recessive phenotype results from a cross between heterozygous parents: Gg x Gg. A Punnett square can illustrate. b) (5 pts) Based on your answer in (a) above, what genotypic and phenotypic ratios are expected in the progeny? (State explicitly for each genotype and phenotype). Genotype ratio - 1 GG : 2 Gg : 1 gg. Phenotype ratio – 3 gray : 1 white. This was intended as a “gimme” from Part A above, but some people made it more complicated than it needed to be. 5) (6 pts.) Mitosis and meiosis are both forms of cell division. Briefly state three ways in which mitosis and meiosis differ. 1. Mitosis o takes place in somatic cells; meiosis only takes place in cells that form gametes. 2. Mitosis involves 1 cell division (2 daughter cells), meiosis involves 2 cell divisions (4 daughter cells). 3. Mitosis leads to genetically identical daughter cells which are identical to the parent cell also; meiosis leads to genetically distinct daughter cells that also differ from the parent cell. 4. Mitosis leads to daughter cells with same ploidy as parent cell; meiosis halves the ploidy of the parent cell. Extra Credit. (2 points) Write a Haiku poem about an evolutionary concept, discovery, or scientist. For those who don’t remember from high school literature classes, Haiku is a style of unrhymed Japanese poetry (but you can write in English) that usually consists of 3 lines: one of 5 syllables, one of 7 syllables, and one of 5 syllables. It avoids use of the first person and also usually mentions a season or time of year (but I’ll accept any sincere attempt).