EXAM II 2014
EVOLUTIONARY BIOLOGY – PART II
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Name
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TA Name
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Lab Day & Time
Negative Points
Positive Points
Page 2
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_______________ 12 pts
Page 3
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_______________ 16 pts
Page 4
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_______________ 12 pts
Page 5
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10 pts
TOTAL
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50 pts
B. B. Fill in the blank with the best answer. Be as specific as possible.
(1 pt each)
_Homeotic___ 1. What do we call genes that control a cluster of other genes during embryological
development?
2. Name a plant that lacks xylem or phloem
Moss, Liverwort
Hornwort
_Co-evolution
3. What do we call the relationship when two species interact, each one modifying the evolution
of the other? E.g. myxoma virus and rabbits in Australia.
_Conjugation or 4. What is the process called when a plastid is passed from one bacterium to another?
Horizontal gene transfer
_Oxygen
5. What is the byproduct of photosynthesis in blue green bacteria?
_Addition or
6. What kind of point mutation could lead to a frame-shift?
subtraction, deletion
_Five (5)
7. If a skin cell of an animal usually has 10 chromosomes, how many chromosomes would its
sperm cell have?
Mitochondrion__
8. Where is O2 used in the eukaryotic cell?
9-12 Using the following chart (where + indicates having a particular trait, and 0 indicates not having a
particular trait), place labeled tick marks appropriately on the tree below.
Hair
Placenta
Binocular Vision
Rumination
Frilled Lizard
0
0
0
0
Koala
+
0
0
0
Gorilla
+
+
+
0
Impala
+
+
0
+
Frilled Lizard
Koala
Impala
Gorilla
2.
C. Definition Questions. Define the following terms or phrase giving an example and answer
the follow up question. Do not be superficial in your responses; give details (4 pts. each)
1) Horizontal gene transfer: The transfer of genes from one species to another.
Example: This can occur by transduction, transformation, or conjugation, typically bacteria. The DNA from one species
gets transferred via say viruses from one species to another
What is the relevance of this phenomenon to evolution and scientists ability to determine phylogenies?
The relevance is that our usual way of thinking about phylogenies is that genes are passed through generations of
organisms and will slowly change via mutation, sex, and crossover, and selection. If horizontal gene transfer occurs,
there is an instantaneous change in the species and the genes can be picked up by distantly related organisms. This will
confuse our normal way of depicting ancestral relationships by way of a tree diagram, which is no longer appropriate.
2) Genetic Drift: is the change in the frequency of a gene variant (allele) in a population due to random sampling
of organisms.
Example: Just by chance in an island population a Tsunami may wipe out the all blue-eyed people and thus leaving
only brown-eyed people as the survivors. Thus brown-eye will forever be fixed in the population.
Under what circumstances can this be more important to evolution that natural selection? Whenever
populations are small, genetic drift can play an important role, such when a population crash occurs or on
islands, etc.
3) Keystone species: This is a species that has a disproportionately large effect on its environment relative to its
abundance.
Example: A beaver building a dam, elephants trampling the trees in a forest, a starfish predator in a tide pool,
wolves in Yellowstone National Park.
Why does it seem critical that wildlife managers keep this concept in mind? Since such organisms play a
critical role in maintaining the structure of an ecological community, affecting many other organisms in an ecosystem
and helping to determine the types and numbers of various other species, their removal will have a dramatic effect
upon the whole community.
4)
Lytic life cycle (Give the steps and explain clearly): This is the life-cycle of many viruses leading to the
death of the host cell. The key steps include 1) the attachment of the virus particle to the host cell; 2) the
penetration of the virus into the host cell; 3) replication of the viral nucleic acid and formation of the protein
capsids; 4) assembly of the nucleic acid and capsids into virus particles; 5) release of the virus as they split
open the host cell and leave to infect other cells.
Example: This is the common way that bacteriophages attack bacterial cells.
What is the critical difference between this cycle and the lysogenic cycle? The critical difference is that
viruses going through the lysogenic cycle do not immediately kill the host cell. The viral DNA integrates into the host
chromosome and remains there and is passed on the every generation of cell as it divides. It only periodically awakens
and then completes the cycle but multiplying and killing the cell as in the lytic cycle.
3.
D.. Short Answer Questions (3 pts each) State whether the statement is true or false and then give the evidence
supporting your claim
1) In mammals, females are usually more selective in their mating preferences than males; this is consistent with the
argument that they have a greater parental investment in their offspring.
True. Females are more selective because they can only have limited number of offspring. They are tied up with
pregnancy for many weeks or months in the case of humans, then they care for the young and feed them for long blocks of
time. In contrast, males are capable of mating numerous times and fathering many offspring. And in many species they do
not participate in the care giving. Typically, there is a large discrepancy in the parental investment between the genders.
2) Biologists have a hard time explaining the altruistic behavior of some animals since it apparently runs counter to
an individuals’ genetic self-interest.
False. Biologists readily explain many altruistic behaviors such as those which involve acts involving relatives (kin
selection). These are acts involving potential self-sacrifice where one individual of a population helps one of his kin at
the potential disadvantage to himself. This has been explained using the argument of inclusive fitness. This means that
biologists recognize that relatives (brothers, sisters, cousins, etc.) all share the same alleles, and if their self-sacrifice aids
in the survival of a number of their kin, even if they perish, their alleles will be passed on. If they did not do this perhaps
all will perish. An example of this is when meerkats post look outs for predators who are vulnerable to be caught but if
they warn the colony in time no one will die. All of the colony tends to be related genetically.
3) Resource partitioning and character displacement explain the fact that two species of birds look rather similar
when they live in different areas, but they look quite different when they live together.
True. When two similar species are competing for the same resources (e.g. food) and they live in different areas, they will
have a relatively large variation in their anatomy and sill survive because there is no interspecific competition. But if they
live together then the individuals which are in direct competition for food will have the most difficulty surviving. Those
individuals which specialize and are therefore have less competition with the other species will be more likely to survive.
Thus the two species tend to become more distinct if they exist coexist together.
4) Some features of organisms are so complex and intricate they are said to be Irreducibly Complex, meaning that
the organ cannot function unless all of the pieces are in place (e.g. the blood clotting mechanism consisting of
dozens of enzymes and products; if anyone is missing the blood fails to coagulate). This is an example of an
Intelligent Designer and that all of the pieces were put into place simultaneously.
False. There are organs such as the eye or systems such as the blood coagulation mechanism that are very complex and
appear to require that all elements be in place in order to work; that is, they don’t seem to have evolved in a step-wise
fashion, such as be required by an evolutionary scenario. But we don’t have to invoke an Intelligent Designer to explain
this. Just because you don’t understand the solution right away, doesn’t mean that we have to invoke a miracle.
Evolutionary explanations are available once the system is studied. For example, we know that human eyes will work
even if they are imperfect albeit not as effectively as a perfect eye. And once we have examined all of the eyes in
organisms such as mollusks, we find an immense number of different types of eye that all work. All of them seem
“incomplete” when compared to the elegant eyes of the octopus or squid. We can easily piece together an evolutionary
sequence leading form the simple to the complex.
3
E. Long Question (10 pts)
Some years ago scientists from Yale reported that some people have an ability to taste a chemical called
propylthiouracil (PROP) and others can’t. A test was administered by having people put a piece of paper laced with
PROP in their mouths for a few seconds. Some people taste a strong bitter flavor, other people taste a mild bitter
flavor, and still others taste nothing at all. This appears to be a genetically determined trait that produces three types
of tasters. Researchers think it depends upon the number of special taste buds on the tongue. Answer the following
questions with explanations. (10 pts.)
a. Is this likely to be a polygene trait? Why?
No, this looks to be a trait determined by two alleles because you only appear to have three phenotypes. A polygene trait
typically has a wide range of phenotypes that follow a bell shaped curve.
b. Can we distinguish between complete dominance, incomplete dominance, and co-dominance in the expression
of the trait? If so how can we do that?
We can go part way to solving this just on the basis of the three phenotypes, one of them (the phenotype where a mild
flavor is detected) seems to be an intermediate of the two others. This suggests that this is either due to incomplete
dominance or co-dominance. Now, if we can determine the molecular mechanisms involved we can figure out which it
is. In co-dominance we would find that both the tasting allele and the non-tasting allele were both active producing
the intermediate condition. In incomplete dominance only one allele would be active but the enzyme it would be
producing would be inadequate to produce the full effect.
c. If 100 people were tested and we found the data shown below, would this suggest that the population is in
Hardy Weinberg equilibrium? Super tasters =16%, medium tasters =48%, and non-tasters =36% . Show your
work.
Let’s suppose that non-tasters had a double recessive genotype , so q2 = .36 and q= 0.6
This means that p= 0.4 and p2 = .16
So p2+2pq+q2 =1 would be 0.16 + .48 + .36 =1 and this does suggest that the population is in Hardy-Weinberg
equilibrium. This would work out the same way even if the supertasters were the double recessive.
d. If the above were true, would you expect either genetic drift or selection to play a strong role in determining
the proportion of individuals with the various tasting abilities?
Since it is in equilibrium, that strongly suggests that selection has not played a role, and it probably will not in the future.
And since the population is small, that strongly suggests that genetic drift will play a role.
e. Suppose that tasting is a dominant trait, if two medium tasters were to have children, what types and
proportions of phenotypes would you expect?
One TT= Super taster; 2 Tt = Medium tasters; one tt= Non- taster