Difference between revisions of "Evolutionary Biology Spring 2011 Study Questions"

Revision as of 16:27, 25 February 2011

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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 20, 2011)

What is speciation?

What are three ways relationships among organisms can be depicted or described?

What is homology?

Explain how the Permian Mass Extinction had a large effect on the diversity of life on Earth. How did that extinction influence the diversity of life present on Earth now?

Describe three different patterns in the diversity of life that evolutionary biology seeks to explain.

Lecture 2 (Jan 25, 2011)

Give an example of the fit between an organism and its environment.

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

Suppose you observe that the average weight of squirrels on campus is greater than their average weight on Horsebarn Hill. Give an example in which this difference in weight is the result of an evolutionary change. Given an example in which this difference is not the result of an evolutionary change. Describe an experiment you could do to determine whether the difference is due to an evolutionary change or not.

What is the relationship between Mendelian genetics and population genetics?

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

In general terms, what genotype frequencies are expected under the Hardy-Weinberg equilibrium?

What happens to genotype frequencies in a population under Hardy-Weinberg equilbrium? What happens to allele frequencies?

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

Lecture 3 (Feb 3, 2011)

While studying anole lizards you observe that some lizards are more green in color (found mainly on tree leaves) while others are more brown in color (found mainly on tree trunks). In order for this phenotype to be an evolutionary change what must be the source of variation? How could you test to see the source of this phenotype variation?

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

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

Why does population size matter when studying population genetics?

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?)

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

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?

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.

Lecture 4 (Feb 8, 2011)

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

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?

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.

In the Continent to Island Migration model, it is assumed that the frequency of the continent allele, pc, stays the same. Why is this a reasonable assumption?

How can you calculate the allele frequency of an island population after 1 generation of migration?

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

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

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

What is the effective population size, Ne, and what is an ideal population?

Lecture 5 (Feb 10, 2011)

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

What are the different types of non-random mating?

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

What is the most extreme form of inbreeding?

How does inbreeding generally decrease fitness?

Inbreeding generally occurs in smaller populations. What other evolutionary change have we studied that also affects small populations more than large ones? How are they similar and how do the two differ on their affect genotype frequencies in the population?

There are many species of plants that are obligate selfers (they can only reproduce with themselves). Why do you think that this is a successful strategy for these plants? (Think about the effects of inbreeding and fitness)

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

How does inbreeding depression affect populations? Give an example of a real example of inbreeding depression.

Lecture 6 (Feb 15, 2011)

What are the 3 premises of the theory of evolution by natural selection?

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

What HWE assumption does natural selection violate?

Why is the relative number of offspring more important when considering an organism’s fitness than the absolute number of offspring?

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

What does w symbolize and how is it calculated?

Calculate the mean fitness of the population of flies we used in our example, and show that the change in allele frequency results in an increase in the mean fitness of the population. (Hint: you'll need to keep track of quite a few decimal places to see the effect.)

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

How do you calculate genotype frequencies and allele frequencies before and after selection?

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.

Lecture 7 (Feb 17, 2011)

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

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

What does a fitness landscape look like for genetic drift?

What is the evolutionary consequence of directional selection?

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

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

How do drift and directional selection act on a population together? How does this interaction change with population size? How does this interaction depend on the strength of selection?

What is the evolutionary consequence of stabilizing selection? How can you predict the equilibrium allele frequencies?

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

Lecture 8 (Feb 22, 2011)

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

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

In the example given today for disruptive selection, the minimum fitness occurred when the allele A frequency was 0.35. Why isn’t the fitness minimum always at an allele A frequency of 0.5, since this maximizes the proportion of heterozygotes in the population?

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?

What is the effect of drift on a small population under stabilizing selection? Predict how a plot of Freq of A vs. generation would change with stronger or weaker selection.

What is phenotypic plasticity?

In Endler’s guppies, why doesn’t drift provide a convincing explanation for the patterns of variation observed in nature?

What were the two kinds of selection that were acting on the guppy populations to produce the color/spot patterns observed in nature? How was this determined?

What are the differences between quantitative and Mendelian traits?

What are the three consequences of traits being determined by multiple loci?

Give two different scenarios in which natural selection is happening, but there is no evolutionary response to this selection.

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 9 (Feb 24, 2011)

What is the phenotype of an organism dependent on?

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

If 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 to phenotype value look like before and after reproduction?

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

If h^2 = 0 then what is variation in the phenotype a result of?

A selection event occurs in a population allowing only some of the individuals to survive. The average trait value of the survivors are 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?

What do the fitness landscapes for directional, stabilizing and disruptive selection look like when multiple loci contribute to a phenotype? How do these fitness landscapes differ from their single-locus counterparts? In the multi-locus case, explain how the same fitness landscape could give rise to directional or stabilizing selection, depending on the initial distribution of phenotypes in the population.

Give two examples of scenarios in which natural selection is acting but there is no evolutionary response to selection.

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.