Download EB omtentaVT2_130615

Umeå universitet
EMG
Barbara Giles
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Examination formalities
Course name: 5BI097 Evolutionary Biology 15 hp
VT13
Date: 2013-06-15
Time: 09.00-15.00
Authorised aids: English – Swedish, English – French, English – Spanish, English – Portuguese,
English – German, English-Bengali lexicons and Pocket Calculators
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RE-EXAMINATION, Evolutionary Biology 2013-04-13
EMG, Umeå universitet
This exam consists of 4 sections. Each section contains the subject areas taught by a given
teacher and reflects the expected ’learning outcomes’ specified in the course plan and given
below.
After participation in this course, students will be able to:
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apply scientific methods within the field of evolutionary biology
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explain the central processes that govern evolutionary processes in natural populations
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understand simple mathematical models of evolutionary processes
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identify and define evolutionary problems – independently summarize, critically analyse and evaluate the
literature within the field
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demonstrate knowledge in written form
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communicate the principles, theories, problems and research results associated with questions that lie within the
framework of the course.
Each section consists of a number of questions. The maximum number of points, the number of points
required for a pass (= 60%) and a pass with distinction (= 80%) are given at the beginning of each
section.
The final grading of the entire exam is based on the following:
• A pass requires that you have obtained a score ≥ 60% in each and every section.
• A pass with distinction within each section requires that your total section score ≥ 80%. This requires
that you have answered in an organised, well-formulated manner that attempts to analyse and/or explain
what you are asked for. Short, point-form answers without logical connectors will not earn you a pass
with distinction, nor will excessively long answers that contain everything you think you remember
written in the hope that it contains something that fits the question.
• A pass with distinction on the entire exam requires that your total score from the 4 sections ≥ 80%,
that you have scored ≥ 80% on at least two sections and that you have passed all sections.
• In the event of failed sections, you must rewrite these sections but you will not be required to rewrite
the sections you have passed.
On this exam: Full marks = 80 points; Pass ≥ 48 points; Pass with Distinction ≥ 64 points.
Write your answers on the official examination paper provided. Note: ANSWER
QUESTIONS FROM DIFFERENT TEACHERS ON SEPARATE SHEETS.
Write your personal examination code on every sheet of paper!
SUBMIT QUESTION & ANSWER SHEETS TO INVIGILATORS
Good Luck!
Barbara, Pelle, Folmer and Xiao-Ru
Umeå universitet 901 87 Umeå. Telefon: 090-786 55 21. Telefax: 090-786 67 05.
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EXAMINATION Evolutionary Biology 2012-04-14
(1) Start by reading through the entire exam. There are 17 questions, spread over 6 pages (pg 4-9). The
exam is worth 80 points. You have 6 hours which is 13 points/hour.
(2) Get a feeling for how many points each question is worth and portion out your time.
(3) Start by answering the questions/sections for which you know the answers (easily earned points for
you) – leave the questions you find most problematic to the end (harder earned points for you). Don’t
panic.
(4) Attempt to answer each and every question; do not be afraid to guess – tell us how you are thinking
and that you are guessing. Guesses will not be penalized, especially if they are explained well. Again, do
NOT write everything you think you remember in the hope that one of your teachers can find something
that fits the question. Shape your answer – show your reasoning!
(5) Some questions may look as though a short phrase may suffice as an answer – we, however, are
looking for your explanation and motiviation of your answer. Again, don’t write down absolutely
everything you know about the subject – demonstrate how you have reasoned in answering the question.
(6) Write clearly so that we can read your answers.
If you have trouble with understanding what a question is asking and we are not there to answer your
question, write down your own interpretation of it and answer that question. Invigilators can contact Barbara
Giles by telephone if there are other problems.
You may answer questions in Swedish or English as you wish.
A LIST OF SECTIONS THAT EACH STUDENT MUST RE-WRITE IS GIVEN ON THE
LAST PAGE OF THE EXAM.
Umeå universitet 901 87 Umeå. Telefon: 090-786 55 21. Telefax: 090-786 67 05.
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Section 1:
Questions from Barbara Giles
Microevolution: Origin of genetic variation, Mendelian genetics in populations, adaptation & selection,
genetic drift & effective population size, migration & population structure, mating systems
Max 20p, Pass = 12p, with distinction = 16p
Mutation:
1. Mutation rates are sufficiently low, per locus per gamete per generation, not to be a strong force in
producing evolution. Yet a close personal friend of yours claims that in fact mutations are very common
in natural populations and therefore mutation rates play a significant role in evolution. Resolve this
paradox. (3p)
2. One often reads about mutations being "random." In what sense are mutations random, and in what
sense are they not? (2p)
Adaptation & selection:
2. Suppose you are studying a population of an animal or plant. You wonder if this population is
genetically distinct from neighboring populations (i.e., an ecotype). Briefly state several ways by which
you could determine if your population is indeed a locally adapted ecotype. Then describe in some detail
how this putative ecotype could have evolved to be distinct from neighboring populations. Include the
concepts of mutation, natural selection, gene flow (migration), genetic drift and inbreeding. (4p)
3. Will the current AIDS epidemic lead to an increase in the frequency of the CCR5 Δ-32 allele within the
near future (the next 100 years)? Explain why or why not (where or where not), using differential
frequencies of HIV infections AND differential frequencies of resistant individuals in populations. The
following diagrams might be helpful in organizing your thoughts. State any assumptions you might be
making about the inheritance of the resistance trait. (5p)
Genetic drift and Migration:
4. Remote oceanic islands are famous for their endemic species – unique forms that occur nowhere else.
Consider the roles of migration and genetic drift in the establishment of new species on remote islands.
Umeå universitet 901 87 Umeå. Telefon: 090-786 55 21. Telefax: 090-786 67 05.
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(a) How do plant and animal species become established on remote islands? Are endemics more likely to
evolve in some groups of plants and animals than others. Which? Motivate your answers! (2p)
(b) Consider a new population that has just arrived at a remote island. Is the population likely to large or
small? Will founder effects, genetic drift, and additional waves of migration from the mainland play a
relatively large or a small role in the evolution of the new island population (compared to a similar
population on an island closer to the mainland)? Choose your answers so that they explain how unusual
endemic species are likely to be more common on remote islands than on islands closer to the mainland.
(4p)
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Section 2:
Questions from Pelle Ingvarsson
Microevolution: Quantitative genetics, detecting selection, evolution of sex & linkage disequilibrium,
sexual selection
Max 20p, Pass = 12p, with distinction = 16p
Evolution of sex & linkage disequilibrium:
5. Sexual reproduction is inherently costly and for sex to be favored over asexual reproduction it must
supply benefits that outweigh these costs. Give two reasons for why sex can be beneficial (2p)
6. In a population of plants flower colour is determined by a single locus, where the C allele codes for red
colour and c codes for white colour. In the same species, petals can either be spotted or plain (nonspotted). This is also single gene trait with P coding for the spotted phenotype and p coding for the plain
phenotype.
The frequency of the 4 possible genotypes in the population are as follows:
Spotted, red-colored flowered (PC): 0.36
Spotted, white-colored flowers (Pc): 0.15
Plain, red flowers (pC):
0.06
Plain, white flowers (pc):
0.43
(a) Calculate the linkage disequilibrium (D) in the population. (1p)
(b) Assume that the observed linkage disequilibrum is caused by natural selection. What conclusions can
you draw about the form of selection acting on flower colour and pattern from the value
of D? (2p)
Sexual selection:
7. Give two factors favoring a monogamous mating system (2p).
Quantitative genetics & Detecting selection:
8. David Lack was a famous British ornithologist who studied clutch size in the Robin (Erithacus rubccula).
Lack counted clutch sizes (i.e. number of eggs laid) from around 1000 nests in 1945 and the data is given
in the histogram in the figure below. Lack also followed all clutches to see how many fledglings (young
that left the nest) were produced from each nest. The red line in the figure below depicts the average
number of of fledglings produced from a given clutch size and can thus be viewed as a measure of fitness
of these birds.
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(a) What type of natural selection is clutch size experiencing? (2p)
(b) Assume that the heritability (h2) of clutch size in robins is 0.65 and that the mean clutch size in the
population is 5 eggs per nest. However the mean clutch size, when taking fledgling success into account,
is 7.5 eggs per nest. Calculate the expected mean of clutch size in the next generation. (2p)
(c) When Lack returned a few years later, in 1951, both the distribution of clutch sizes and the number
of fledglings per clutch looked exactly the same as in the figure above (i.e. neither of them had shifted
from the observation in 1945). Give at least two alternative explanations for this observation? (4p)
9. During the early part of the 20th century, Danish geneticist Wilhelm Johannsen performed a series of
experiments that helped shape our understanding of how quantitative traits are inherited. In one of his
most famous experiments he inbred a number of lines of the common bean (Phaseolus vulgaris) by selfing
for 10 generations. Using this data he was able to estimate the genetic and environmental variation for
seed weight to be 56.7 and 32.1, respectively.
(a) Calculate the heritability of seed weight for Johannsen's experiment (2p)
(b) If you were to repeat Johannsen's experiment today, using the same species, do you think that you
would get the same heritability again? Motivate your answer (3p)
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Section 3:
Questions from Folmer Bokma
Microevolution: Life history evolution
Macroevolution: Sequence evolution, phylogenetic analyses
Max 20p, Pass = 12p, with distinction = 16p
10. Suppose you are interested in investigating whether in a group of species a particular phenotype
evolved gradually over time (fig. b), or suddenly when new species appeared (fig. a).
(a) What term is used for the pattern of evolution shown in panel (a), where phenotypes change quickly
when a new species appears, to subsequently remain largely unchanged until the species goes extinct?
(2p).
(b) What term is used for the lack of change in the morphology of species over time between speciation
events? (i.e. the phenomenon of vertical lines in panel (a)) (2p)
11. Darwin explained the long nectar spurs of the Madagasy orchid Angraecum sesquipedale as the result
of an arms race with a hawkmoth: moths with very long tongues get nectar from flowers with relatively
short spurs without pollinating these flowers. Consequently, flowers with longer spurs have higher
fitness, but as over the course of evolution the flowers get longer tongues, the moths need to develop
longer spurs. Do you think this is a good explanation of the long spurs of Angraecum sesquipedale?
(Motivate your answer.) (3p)
12. According to panel a in the figure of question 10, morphological evolution of species does
not proceed gradually in small steps over time, but by rapid jumps during or immediately
following speciation, followed by long periods in which change is virtually absent. Some
researchers claim that this is not in line with Darwin's idea of evolution by natural selection.
Others disagree, saying that rapid change can be explained by directional selection, and lack of
change by stabilizing selection.
(a) What is your view on this, and why? (5p)
(b) How could you, using a phylogeny of species in the genus Angraecum, determine whether the length
of nectar spurs evolves gradually over time, or by sudden jumps associated with speciation? (2p)
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13. The fossil record indicates that most species that have existed on earth, are now extinct. One could
envision a different scenario, in which species continuously adapt to changing conditions, and never go
extinct. Why do species go extinct? (6p)
Umeå universitet 901 87 Umeå. Telefon: 090-786 55 21. Telefax: 090-786 67 05.
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Section 4:
Questions from Xiao-Ru Wang
Microevolution: Speciation
Macroevolution: Plant systematics & evolution
Max 20p, Pass = 12p, with distinction = 16p
Speciation:
1. This graph plots degree of prezygotic isolation versus genetic distance in a variety of sister-species pairs
of Drosophila. Prezygotic isolation is estimated from mate-choice tests. A value of 0 indicates the different
populations mate freely (0% prezygotic isolation) and 1 indicates no interbreeding (100% prezygotic
isolation). Genetic distance is estimated from differences in allele frequencies.
What can you conclude from this graph plot? What order of speciation events does this graph plot
reflect, and explain why? (5p)
2. What would be the possible outcomes when two populations that have long been isolated
geographically come back into contact, and under what conditions does each outcome occur? (5p)
Plant evolution and diversification:
3. Why is hybrid speciation more common in plants than in animals? What are the main modes of hybrid
speciation, and which one is more commonly observed, and why? (5p)
4. Tracheophytes (Vascular Plants) have several evolutionary advances that made them better suited for a
fully terrestrial existence than are the Bryophytes. Please identify at least five adaptive traits and their
functions that facilitated the proliferations of vascular plants on land. (5p)
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