The following are the homework questions for Organic Evolution for Fall, 2000. BE SURE you have read the information on homework assignments BEFORE completing any of these questions! Remember that you will be graded on both content and presentation (grammar and style.) Be sure to send your e-mail from the address to which you wish your graded homework returned. Answers will be posted after the homework has been turned in. Remember that you must include your homework within the body of an e-mail message (DO NOT present it as an attachment) and that the subject of your message MUST be in the format HW# your name (e.g. HW1 Rebecca Irwin) -- otherwise I may not find your homework answer while I'm grading them. Remember that it is YOUR responsibility to keep a copy of your homework answers until you receive your graded homework back (in case it doesn't get to my computer for some reason.)
Homework Question #1: e-mail a complete answer to the following question to me at rirwin@utm.edu by the due date given in the syllabus.
Vascular tissue (the tissue that transports water and nutrients) in plants is thought to improve the the ability of plants to use dry habitats on land. Clearly explain how vascular would have evolved through natural selection, assuming that the ancestral plant species did not have vascular tissue. In your answer, use and define the terms fitness and adaptation and make it clear how they apply to this situation. To explain how vascular tissue would have evolved through natural selection, use all four of Darwin's four postulates, and make it clear how each would have applied to this case, and resulted in the evolution of vascular tissue through natural selection.
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Homework Question #2: e-mail a complete answer to the following
question to me at rirwin@utm.edu by the due date given in the syllabus.
The narrator of a nature show on TV describes insects as more advanced evolutionarily than earthworms and describes insects as having many adaptations that have evolved to promote the survival of their species. Describe THREE ways in which these statements do NOT make evolutionary sense; fully explain (including all logical steps) why these statements do not make evolutionary steps.
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Homework Question #3: e-mail a complete answer to the following
question to me at rirwin@utm.edu by the due date given in the syllabus.
NOTE: typing answers to math problems can be painful but please try to
type a clear answer to this question; it will help you to review the way
these questions work. Since most e-mail doesn't support superscripts
(for writing something squared, like p2) or square root symbols
or lines over letters, you can write p^2 for p2 , sqrt
() to indicate the square root of something, and "wbar" for the average
population fitness (typically symbolized by a w with a line over it).
SHOW ALL FORMULAS USED AND MATHEMATICAL STEPS. Round to two significant
figures.
Here's the question: Consider two genes in a large, randomly mating population of a species of grass in which there no movement of individuals in and out of the population and no mutation. The two alleles at one gene, D and d, do not affect grass survival or reproduction. The two alleles at the other gene, R and r, do affect grass survival and reproduction by affecting the degree to which the grasses resist the harmful effects of a naturally occurring heavy metal ion in the soil. RR individuals and Rr individuals both have a mechanism of detoxifying the heavy metal ions and have high survival (RR and Rr individuals survive equally well.) rr individuals do not have a mechanism of detoxifying the heavy metal ions and survive to reproduce only 1/15 as well as do the individuals who do have the detoxifying mechanism. Answer the following parts to the question:
Homework #4 e-mail a complete answer to the following question to me at rirwin@utm.edu by the due date given in the syllabus.
Contrast the amount of genetic variation predicted to be present in the following two populations and clearly explain why they would differ in genetic variation; base your answer on the predicted levels of gene flow and genetic drift for the situations given (be sure to indicate how much drift and how much flow is predicted for each population, and why they would result in the predicted levels of genetic variation.)
Population 1: a small population of pine trees on an island that
is distant from other islands so that pine pollen and pine seeds almost
never arrive on the island from anywhere else.
Population 2: a large population of maple trees surrounded by
other populations such that the wind frequently blows maple seeds from
population to population
Homework #5 e-mail a complete answer to the following question to me at rirwin@utm.edu by the due date given in the syllabus.
In a population of hawkweed plants, you observe continuous phenotypic variation in two traits: flower color ranges from pale yellow to dark orange (with a continuous range of intermediate shades of yellow and orange) and leaf size. Flower color affects how well the flowers attract pollinators; the insects that pollinate these flowers have remained in constant abundance for hundreds of generations and are most attracted to bright orangy-yellow flowers. Leaf size determines how well the plants tolerate different levels of environmental moisture: small leaves are most drought resistant but large leaves do best in wet years. Where these plants occur, the moisture level of the climate is extremely variable -- some years there is almost no rain and other years it pours for months on end. You are going to conduct a mid-parent offspring regression to study the heritability of each of these two traits. Clearly explain how you would conduct this. Which trait (flower color or leaf size) would you predict to have high heritability and which trait would you predict to have low heritability? Explain why. Describe the results you expect to obtain from the mid-parent offspring regression (remember that your results will be a graph, so you should describe what the graph looks like) if you are correct in which you predict to have high heritability and which you predict to have low heritability.
Homework #6 Answer this question based on section 3.2 (pp. 78-83) in your textbook as well as your lecture notes:
What is linkage disequilibrium? Compare and contrast the concepts of linkage disequilibrium and correlated characters. Explain how linkage disequilibrium can be caused by physical linkage (explain what this means.) How does the evolution of traits in linkage disequilibrium differ from the evolution of traits in linkage equilibrium?
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Homework #7 e-mail a complete answer to me by the due date given on the lecture syllabus
You are studying the phylogeny of a group of species of angiosperm (flowering
plant.) Some of these species have brightly colored petals; others
do not. It turns out that having brightly colored petals is primitive
in this group, while lacking brightly colored petals is derived.
Which character state -- presence of brightly colored petals or absence
of brightly colored petals -- can provide information about how these species
are phylogenetically related to one another? Clearly explain why by explain
why one form of character state (primitive or derived) can provide evidence
for phylogenetic relationship while the other form of character state (primitive
or derived) can not.
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Homework #8 e-mail me a complete answer by the due date given on the lecture syllabus
You are continuing to study the group of angiosperm species you started studying last week. You have collected information on many additional morphological characters and are now considering whether to study DNA sequence variation as well. Explain why it can be a good idea to study both DNA variation and morphology for your phylogenetic analysis by describing one reason morphological characters may be unreliable with regard to phylogenetic analysis that is not predicted to apply to DNA data, and one reason DNA sequence variation may be unreliable with regard to phylogenetic analysis that is not predicted to apply to morphological data.
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Homework Question #9: e-mail me a complete answer by the due date given on the lecture syllabus. NOTE THAT FOR THIS WEEK you need to complete TWO homework questions, both #9 AND #10, since there are no lab meetings this week.
You have completed a DNA sequence based phylogeny of angiosperm species and would like to use the molecular clock to determine dates of speciation. What additional information do you need (beyond the DNA sequences of the species you are studying); how would you obtain that information and how would you use it to determine the dates of speciation? The dates of speciation you determine using the molecular clock hypothesis are only valid if the main assumption of the molecular clock hypothesis is true: what is that assumption and how would you use the phylogeny you have obtained to test that assumption?
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Homework #10. e-mail me a complete answer by the due date given on the lecture syllabus. NOTE THAT FOR THIS WEEK you need to complete TWO homework questions, both #9 AND #10, since there are no lab meetings this week.
Within many plant groups, there are forms of plants that are very ecologically and morphologically distinct from each other, but that can reproduce with each other and produce healthy fertile offspring. Give an argument in favor of classifying such forms together as a single species. What species concept are you using if you do that? Give an argument in favor of classifying such forms as separate species from one another. What species concept are you using if you do that?
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Homework #11. e-mail me a complete answer by the due date given on the lecture syllabus.
You are comparing a group of plant species with flowers pollinated by insects that specialize on particular flower types with a group of plant species with wind pollinated flowers. Assuming there are no other relevant differences between these plant groups, within which group would you expect more of the speciation to have been sympatric? Explain why.
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Homework 12. e-mail me a complete answer by the due date given on the lecture syllabus.
State the three steps of the Oparin-Haldane model of the origin of life on earth. Illustrate the first two steps by stating a specific molecule that would have formed during that step, and briefly stating one hypothesis for how it would have formed. For the third step, indicate why one form of molecule, either DNA, RNA, or protein, is thought to be the most likely candidate for that step.
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Homework 13. e-mail me a complete answer by the due date given on the lecture syllabus.
On the following phylogeny, the letters indicate the points at which each of four characters originated. Which character (w, x, y, or z) is most likely to be a key innovation? Clearly explain why; in your answer, explain what a key innovation is, what results after the evolution of a key innovation, and why the character you selected best shows this predicted result.
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Homework 14. e-mail me a complete answer by the due date given on the lecture syllabus.
In some species of earwig (a kind of insect), developing individuals initially grow rudimentary (small, non-functional) wings; later, they develop into forms with fully developed, large wings. Other species initially develop rudimentary wings and then retain these throughout life, never developing functional wings. The relationships of earwigs to other insects are not clear; they could be related to either forms with well developed wings or forms without wings. You conduct a phylogenetic analysis to study this problem and your results suggest that earwigs are most closely related to a group that develops large, fully functional wings after an initial stage with rudimentary wings. Based on this analysis, is the evolutionary change in wing structure within the earwigs most likely a result of paedomorphosis or of terminal addition? Explain how you can tell.
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Homework 15. e-mail me a complete answer by the due date given on the lecture syllabus. NOTE THAT FOR THIS WEEK you need to complete TWO homework questions, both #15 AND #16, since there are no lab meetings this week.
Termites and cockroaches are thought to be closely related insect groups; both are diploid, but termites have highly developed altruism and cockroaches do not display altruism. State one possible way that the ecology of the two groups could differ so that altruism would evolve in termites but not in cockroaches. Relate this possible difference to one of the terms in Hamilton's Formula (br-c>0); clearly explain why the difference you propose would affect this term AND explain why this term is included in Hamilton's Formula (why what this term represents is something that must be considered to explain when altruism will evolve; note that simply stating whether it makes the formula greater than zero or not is NOT an explanation of this.)
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Homework 16. e-mail me a complete answer by the due date given on the lecture syllabus. NOTE THAT FOR THIS WEEK you need to complete TWO homework questions, both #15 AND #16, since there are no lab meetings this week.
In a species of insect, you find that some populations reproduce sexually while others reproduce asexually; phylogenetic analysis indicates that both states (sexual reproduction and asexual reproduction) have evolved independently several times. State two hypotheses that could explain this pattern; one must be based on the predicted impact of parasites on the evolution of sex (you need to explain this impact) and the other on something else.
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Upon what kind of DNA sequences have the phylogenies of humans and great apes discussed in lecture been based? Why are they based on this kind of DNA sequence rather than some other area of DNA -- what makes this kind of DNA sequence the most appropriate for studies of this group? What potential problem that could make these phylogenies unreliable is present in this kind of DNA sequence?