Evolutionary Biology Spring 2015 Study Questions

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The following study questions are designed to help you think about the lecture material. They are not comprehensive questions. Exam material is NOT limited to the topics in study questions and will not follow this format.

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Lecture 1 - Jan 20th 2015

1) What type of adaptation would you expect to see in an organism trying to survive in an environment with visual predators?

2) What’s one possible explanation for powered flight appearing only once in invertebrates and at least three times in vertebrates?

3) Why would it be advantageous for an organism to resemble something else; i.e. a caterpillar that looks like bird droppings or an orchid that smells like carrion?

4) What’s convergence? Can you think of an example we saw in lecture?

5) Do similar traits always evolve to solve the same challenges? For instance, are all brightly colored organisms just trying to get a mate?

6) In what ways can humans be a source of selection to other organisms?

7) What’s the difference between evolutionary change and phenotypic plasticity?

Lecture 2 - Jan 22nd 2015

1) Suppose you observe that the average weight of squirrels on campus is greater than their average weight on Horsebarn Hill. Describe how you would use a reciprocal translocation experiment to test the hypothesis that the difference in weight of squirrels on campus and on Hosebarn Hill is the result of an evolutionary change. Explain what outcome(s) would support this hypothesis. What outcome(s) would not support the hypothesis?

2) In class, we focused on figuring out how to tell if a phenotypic difference was caused by an evolutionary change. What if there's no phenotypic difference between two populations you observe in the wild--could there still have been an evolutionary change? Why or why not?

3) Why do we focus on genetic differences in studying evolutionary change?

4) What is the relationship between Mendelian genetics and population genetics?

5) What are the variables used to describe the genetic composition of a population?

6) In general terms, what genotype frequencies are expected under the Hardy-Weinberg equilibrium with 2 alleles? What do you think the proportions are going to be if we’re studying a locus with 3 alleles? Trying drawing one of those box diagrams we saw in class to support your answer.

7) What happens to genotype frequencies in a population under Hardy-Weinberg equilibrium in subsequent generations? What happens to allele frequencies?

8) Hardy-Weinberg practice: try the Pdficon small.gif problems here to get practice with describing the genetic composition of a population and determining Hardy-Weinberg proportions.

9) Challenge Problem: What’s the highest frequency of heterozygotes that is expected under HWE for a locus with 2 alleles?

Don’t forget to finish Activity 2 – It should be handed in at the beginning of lecture on Thursday Jan. 29th.

Lecture 3 - Jan 29th 2015

1) Why do we use allele and genotypes frequencies instead of the number of gametes or individuals in a population?

2) How many generations does it take for a population to establish genotype frequencies in HWE (Hardy-Weinberg equilibrium) given all the assumptions are met?

3) In what situation do we need to assume Hardy-Weinberg equilibrium instead of testing for it? What information do we need in order to test for HWE?

4) HWE assumes that there is no new genetic mutations. However, all new genetic variation occurs through mutation. Why do we mostly ignore this assumption violation?

5) You observe the genotype frequencies of a cow population for 2 generations. The allele frequencies and genotype frequencies do not change. Is this population in HWE? Why or why not.

6) What happens to genetic variation, allele frequencies, and genotype frequencies as a result of inbreeding?

7) What are the different types of non-random mating?

8) How can you tell the difference between inbreeding and assortative mating?

9) What is the most extreme form of inbreeding?

10) What do you expect the effects of inbreeding would generally be on fitness? Why?

11) Why are inbred lines of model organisms (e.g. Drosophila, mice, C. elegans) often used in biomedical research?

12) Under what conditions would assortative mating cause evolution? Under what conditions would it not result in evolution?

13) Given what you know about the different types of non-random mating and their effects on genotype and allele frequencies, what would you expect to be the result of disassortative mating?

There are very good practice questions at the end of each chapter of the textbook. Try doing questions 1 through 5 at the end of Chapter 9 - page 255

Lecture 4 - Feb 3rd 2015

1) Give an example of assortative mating in which mates are NOT chosen by the way they look. What other types of phenotypic characteristics can also be used to choose mates?

2) Assortative mating by size is very common in nature. Can you think of any explanation for why this type of preference arises so frequently?

3) What’s the Wahlund effect? How does it affect the genetic diversity of a population?

4) Is the pattern produced by the Wahlund effect more similar to that observed for inbreeding or assortative mating? How does it differ from that pattern?

5) Why does population size matter when studying population genetics?

6) What effect does genetic drift have on: (a) genetic variation (b) genotype frequencies (are they in Hardy-Weinberg proportions or not? Do they change from generation to generation?)

7) What does it mean when an allele has ‘been fixed’ or ‘gone to fixation’ in a population?

8) If an A allele has a frequency of 0.95 in a population, will this always fixed through drift? What is the probability the A allele will be fixed?

9) One of the consequences of small population size is a tendency to mate with close relatives. What other evolutionary change have we studied that also affects small populations more than large ones? How are these processes similar and how do the two differ on how they affect genotype frequencies in the population?

10) What’s the effect of genetic drift in the genetic diversity of individuals belonging to the same population? How about on individuals belonging to different populations?

11) Given what you know about genetic drift, what’s most likely to happen to a new mutation in a small population? How about in a large (infinite) population?

Lecture 5 - Feb 5th 2015

1) Which assumption of the HWE do both mutation and migration violate and why?

2) What is migration in an evolutionary sense and why is it important for understanding evolution in populations? Give an example of migration and explain its effects on allele frequencies.

3) Why is it important to consider the effects of migration and drift together?

4) How many migrants does it take to keep populations from diverging? Why is this the same for small and large populations?

5) What factor(s) affects the rate of homogenization of allele frequencies when populations are connected by migration?

6) How does inbreeding depression affect populations? Can you think of a real example of inbreeding depression?

7) What level of genetic diversity do we expect to see in a population that has been through a bottleneck? What evolutionary forces are at play in this case? If nothing changes, what’s the ultimate fate of this population?

8) Imagine you are hired by the US government to take part in a conservation effort as a consultant. What aspects of a population’s structure do you have to consider in order to maximize maintenance of genetic diversity? How would you explain to government representatives why it is crucial to maintain genetic diversity?

9) What’s the impact of habitat fragmentation on genetic diversity? What are the evolutionary processes that contribute to that scenario?

Lectures 6 & 7 - Feb 10th and 12th 2015

1) What are the premises of the theory of evolution by natural selection?

2) What is the difference between natural selection and evolution by natural selection?

3) What is artificial selection? Give examples of organisms that have been artificially selected.

4) What do evolutionary biologsts mean when they talk about the fitness of an individual?

5) What HWE assumption does natural selection violate?

6) How do natural selection and genetic drift affect phenotypes? Give an example of when genetic drift and natural selection could be acting on a population.

7) Imagine one of your family members is really curious about what you are learning in this class. How would you explain to him/her how natural selection increases the frequency of an advantageous trait in a population?

8) Can natural selection act on a population with very little genetic diversity (most loci have one fixed allele)?

Lecture 8 - Feb 17th 2015

1) Thinking about the examples of natural selection in action we saw in lecture, what’s the source of selection pressure for the guppies? How about for the Darwin finches in the Galapagos?

2) How do we know the increase in bill depth in the Darwin finches example is a result of evolution by natural selection instead of genetic drift?

3) Can evolution happen from one generation to the next? In order words, can evolution happen in a short period of time?

4) Why do organisms have to be constantly changing in order to increase (or maintain) their fitness? How come different phenotypes can be the fittest in different geographical areas or at different points in time?

5) What are the three modes of natural selection? What’s the evolutionary consequence of each of them and how are they affected by initial allele frequency?

6) What is Fisher’s Fundamental Theorem and why is it important?

7) What does w symbolize and how is it calculated?

8) If the most fit genotype is the heterozygote, why does natural selection lead to the decrease of heterozygotes in the entire population?

Lecture 9 - Feb 19th 2015

1) What are the three types of selection covered in lecture and what is the relative fitness of heterozygotes for each type?

2) Which genotype is most important for predicting a population’s future?

3) What is the evolutionary consequence of directional selection?

4) What is the effect of the starting allele frequency on its fate under directional selection?

5) How does a trait’s dominance influence its fate in a population?

6) What do you predict is the evolutionary consequence of disruptive selection?

7) Why do we say natural selection is short-sighted? Explain.

8) What is a fitness landscape? What are the axis labels?

9) Which type of selection has an outcome that is dependant on the starting frequency of allele A?

10) In a population experiencing evolution as a result of disruptive selection, how would you expect observed genotype frequencies to compare to those expected under Hardy-Weinberg equilibrium in zygotes? What about in adults?

11) What are the differences between quantitative and Mendelian traits?

12) What are the four consequences of traits being determined by multiple loci?

13) Suppose a population has a normal distribution of some trait, the trait is heritable, and only members with above average trait values were allowed to reproduce. What would the trait distribution look like in the following generation?

Lecture 10 - Feb 24th 2015

1) What is the phenotype of an organism dependent on?

2) How is heritability defined? What are two different ways you could measure it?

3) In a scenario which a phenotype has a normal distribution and only individuals with above average traits reproduce. The trait is heritable and after one generation the average of the trait is larger than in the original population. What would the graph of number of individuals vs. phenotype value look like before and after reproduction?

4) What do R and S stand for and how do you calculate them?

5) If h2 = 0 then what is variation in the phenotype a result of? What if h2 = 1?

6) A selection event occurs in a population allowing only some of the individuals to survive. The average trait value of the survivors is different than the original population. You know the heritability of the trait and calculate S and R. What happens to the mean trait value in the next generation relative to the original population's mean trait value when R is positive? negative?

7) Even though natural selection leads to an increase in the mean fitness of populations, it does not always result in a population that has maximum fitness. Explain why not.

8) How is sexual selection different from non-random mating?

9) What are intrasexual and intersexual selection? Give an example of each.

10) What is the common consequence of sexual selection in a population?

11) What is sexual dimorphism? Give a real life example not covered in class.

12) What could be a direct benefit of female choice? What could be an indirect benefit of female choice?

Lecture 11 - Feb 26th 2015

1) So far we have focused on selection on individuals and how it impacts the frequency of advantageous traits in a population. What other levels can selection act on, besides individuals?

2) What are the arguments in favor of selection at the gene level?

3) What is an example of conflict for selection at the gene level?

4) In the example of selection at the organelle level presented in class, what was the organelle in question? What mechanism allowed flowers to produce functional anthers again?

5) Can selection act at the cell level? What’s a good example of conflict between selection at the cell level and selection at the individual level?

6) What are the arguments in favor of group selection? What are the arguments against it?

7) According to Hamilton’s Rule, would an individual be more likely to share its resources with full-siblings or cousins? Why is that so?

8) Why is it advantageous for a female lion to help raise her sister’s offspring?

9) What is an explanation for how eusociality arose in certain insects?

10) Does eusociality have a single origin or has it arisen multiple times?

11) During activity 12, you were asked to choose between two strategies: sharer or monopolizer. Which one had better individual mean fitness? How about the group’s overall mean fitness? In the second part of the game, sharers slightly changed their strategy to what we call tit-for-tat. How did that change both individual mean fitness and the group’s overall mean fitness? What is an example of tit-for-tat occurring in nature?

12) Can selection act at the level of species/lineages? What is the difference between differential speciation and differential extinction? What do they have in common (think about it in terms of number of extant lineages as a result)?

13) Evidence suggests that lineages comprised of asexual organism tend to be younger than lineages of sexual organisms. What is an explanation for this observation? How can sexual reproduction allow a lineage to persist longer in time?

Lecture 12 - Mar 03rd 2015

1) What are the three explanations for the evolution of female preference?

2) In the Runaway Sexual Selection explanation how does the female preference become more common in the population?

3) What is the “Good Genes Model” of sexual selection? Does it rely on the role of direct or indirect benefits to the female?

4) Could the Bird of Paradise courtship display that we watched in class a few weeks ago (watch it again here) be a result of the direct phenotypic benefit explanation to female preference? Could it be a result of the other two explanations of female preference? (This link on female choice might be helpful)

5) What are the four assumptions of Hardy-Weinberg Equilibrium ? What evolutionary forces violate each of them and how?

6) What factors have likely been responsible for divergence in Ensatina? In general, what factors tend to promote divergence of populations? What factors tend to prevent divergence? What evidence is there that color pattern is adaptive in Ensatina?

7) Why is Ensatina treated as a single species even though the southern forms are reproductively isolated from each other?

8) How could gene flow occur from the southernmost inland population to the southernmost coastal population if there is no reproduction between these two populations? (Hint: what other populations are they exchanging genes with?)

Lecture 13 - Mar 10th 2015

1) Why is it important to study reproductive isolation?

2) What is the defiition of the term speciation?

3) Is reproductive success easy to achieve? What are some of the obstacles to successful mating?

4) What are the two types of barriers to reproductive success? How do they relate to the obstacles you talked about in the previous question?

5) What are some of the ways two populations can be reproductively isolated from one another other than geographically? Think about time and space!

6) How important is courtship in animals? What is the function of courship?

7) What aspects of an organism could result in mechanical barriers to reproduction?

8) How is species recognition done in plants? What role can pollinators play in repriductive isolation of plants?

9) How about animals that release their gametes in the environment? How can species recognition happen at the gamete level?

10) What are some of the issues that could hinder proper zygote development?

11) Two populations of individuals belonging to different species produce viable hybrids. In general, what would you expect the fitness of the hybrids to be, relative to the parental individuals? What type of reproductive isolation is this?

12) Does reproductive isolation happen quickly in one step or is it a gradual process?

13) What is the minimum number of incompatible genes required for the establishment of reproductive isolation? (Dobzhansky-Müller incompatibily – check textbook)

Lecture 14 - Mar 12th 2015

1) What is a species? Is the concept of species an easy one to determine? What makes it so complex?

2) What are some fo the reasons why it is a good idea to give species names? What do species represent in nature?

3) What are some of the most important species concepts we talked about in class? How do they differ from one another? What are the issues associated with each of them?

4) Is describing a species a simple procedure? What do we have to know about a group of organisms in order to apply Templeton’s Cohesion Species Concept?

5) What kind of information do we use to recognize species? Is it only about what organisms look like?

6) Do different species mate with one another? Do they produce hybrids? If so, does it mean they are not “good” species? What do the Kikihia cicadas tell us about hybridization in nature?

7) What does the Barcode of Life project do? What kind of data do they use to identify/recognize species?

Lecture 15 - Mar 24th 2015

Lecture 16 - Mar 26th 2015

Lecture 17 - Mar 31st 2015

Lecture 18 - Apr 02nd 2015

Lecture 19 - Apr 09th 2015

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