Download Malthus provided a key idea to both Darwin and Wallace in the

Evolutionary Genetics Midterm 2006
Name
Student #
Signature
The Rules:
P1:
/15
P2:
/22
P3:
/16
P4:
/25
P5:
/22
TOT:
/100
(1)
Before you start, make sure you’ve got all five pages of
the exam, and you’ve written your name legibly on each one.
(2)
Show your work on calculation questions. Feel free to use
the back of the paper if required, but make sure to tell us when
to look on the back. Calculations are required for full credit
where asked.
(3)
If a calculation question requires you to start with the
result from a previous calculation, and you were unable to
answer the earlier question, you may make up a reasonable number
to start with and still potentially get full credit on the
second question.
1. (3 points) True or False: "Evolution requires that some types of individuals are more likely to
survive."
2. (3 points) True or False: "Because mutation rates are very low, mutation contributes little to the
process of evolution."
3. (3 points) True or False: "The main difference between Darwin’s and Wallace’s views of evolution
was that Darwin considered biogeographical patterns to be important."
4. (6 points) Provide three reasons why the frequency of allele A might increase from one generation
to the next within a haploid population. [Explain each answer in one sentence.]
a) Reason:______________ Explanation: ______________________________________
______________________________________________________________________
b) Reason:______________ Explanation: ______________________________________
______________________________________________________________________
c) Reason:______________ Explanation: ______________________________________
______________________________________________________________________
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Evolutionary Genetics Midterm 2006
5.
Name
(10 points) In the Cody and Overton (1996) study, the authors found that Vp/Va (= volume of the
pappus to the volume of the achene shown at left) was greatest for newly
colonized islands and decreased over time since
colonization, as shown in the graph to the right
(note that “mld” denotes the mainland
population). For island populations of the same
age since colonization:
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
a) How would you predict the trends in Vp/Va
to differ on bigger islands versus smaller islands? [Justify your
answer in one or two sentences.]
b) Would you predict Vp/Va to be larger or smaller on newly colonized islands that are closer to
the mainland? [Justify your answer in one sentence.]
6.
(12 points) You are considering the long-term effects of the ozone hole on the genetic health of a
diploid plant population. In the following, consider a gene subject to recurrent mutation, where the
deleterious mutations have selection coefficient, s, and dominance coefficient, h. [Support your
answers with calculations. Do not use your answer to part a) in the other parts.]
a) If more solar radiation enters through the atmosphere, the mutation rate  at the gene might
increase by a factor F to F . What is the new equilibrium frequency of heterozygous
individuals carrying the deleterious mutation?
b) Imagine that the deleterious mutation reduces the evaporative cooling ability of the plant. In
this case, the selection coefficient, s, might increase by a factor C to C s. What is the new
equilibrium frequency of heterozygous individuals?
c) As in b), imagine that the deleterious mutation reduces the evaporative cooling ability of the
plant, so that s increases by a factor C to C s. What is the new equilibrium mean fitness of the
diploid population?
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Evolutionary Genetics Midterm 2006
Name
7. (16 points) A group of researchers has developed a new breed of highly valuable black tulips.
They produce a large number of bulbs from parents of known genotype for unveiling at the annual
garden show. They expect all the flowers to be black, but when the flowers open, they discover
that 6 of their 15,000 plants have even more valuable pale blue flowers. Upon returning to the
nursery, they determine that their pale blue plants are heterozygotes for a white flower mutation
(that is, BB individuals are black, Bb individuals are pale blue, and bb individuals are white). [Show
calculations for parts a, b and d.]
a) Based on these data, what is the mutation rate, µ from the black allele to the white allele ?
b) The relative fitnesses of the three flower types are given by WBB = 1, WBb = 0.88, Wbb =0.76
Calculate the dominance coefficient h and the selection coefficient s for the white allele, b.
c) Using the above fitnesses, is the white allele, b, dominant, partially dominant, additive,
partially recessive or recessive to the black allele, B?
d) If artificial selection practiced by the farmers increases the fitness of pale blue flowers by 50%
(to WBb = 1.22), what would the equilibrium frequency of the black allele, B, be? [Show your
calculations and ignore mutation for this part.]
8.
(10 points) Barrett et al. (2006) maintained 200 lines of the haploid bacteria, Escherichia coli, for
10 days (110 generations). Each line started from a genetically identical stock and was maintained
at a population size of 800,000. The authors then searched the evolved lines for signs that a
beneficial sweep had occurred. Their method (using neutral markers) allowed them to detect
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Evolutionary Genetics Midterm 2006
Name
beneficial mutations that reached a frequency of 45% within this time frame. Assuming that a
beneficial mutation started out at a frequency of 1/800,000, what is the minimum fitness advantage
of a beneficial mutation that the authors could have detected? [Show your calculations.]
9. (15 points) A population of white-tailed deer that has existed on the small island of Vance is being
relocated to the neighbouring island, Juniper, by wildlife managers. 45 deer are moved from Vance
and added to the 78 deer already on Juniper. Genetic data show that these populations are
genetically differentiated at two loci. The Vance population is fixed for alleles Spota and Tailb. The
original Juniper population is fixed for the alternate alleles, Spotb and Taila .
a) Estimate the amount of linkage disequilibrium in the new population immediately after the
movement of adults from Vance to Juniper. [Support your answer with calculations.]
b) If the rate of recombination between the two loci is 0.3, what formula predicts the level of
linkage disequilibrium after one generation of recombination and what is the predicted value
of D (assuming random mating and no selection)?
c) In the absence of selection on either locus, do you expect the allele frequencies to change after
one generation of recombination? Explain in one or two sentences why or why not.
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Evolutionary Genetics Midterm 2006
Name
10. (12 points) A strain of mice was selected for decreased blood cholesterol levels. Over five
generations, the mean blood cholesterol level of the mouse population decreased from 2.16 mg/ 100
ml to 2.01 mg/ 100 ml. The selection differential over this time period averaged 0.07 mg/ 100 ml
per generation.[Support your answers with calculations.]
a) What is the narrow sense heritability, h2, for blood cholesterol levels in this strain?
b) If the phenotypic variance in the population at the start of the experiment is 8.35, what is the
estimated additive genetic variance for blood cholesterol levels?
c) After another 100 generations of selection using the same selection differential, the strain
shows no further response to selection, and blood cholesterol levels plateau at around 1.92 mg/
100 ml. In two sentences, explain what could account for this phenomenon and what might
allow the population to respond to selection once again.
11. (10 points) Describe the principle introduced by Thomas Malthus and how Darwin used this
principle to argue for evolution by natural selection. [Do not use more than the space below.]
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