Biol 211, Fall 2008
Exam #3
Name ____________________
Section 1. Questions in this section can be answered with one or a few words.
For the following definitions, provide the correct term.
1. A gene at one locus alters the phenotypic expression of a gene at a second locus. (1 pt)
[epistasis]
2. Organelle that organizes the microtubules that form the mitotic spindle. (1 pt)
[centrosome]
3. Variations in phenotype based on whether the chromosome was inherited from the mother or from the
father.(1 pt)
[genomic imprinting]
4. Loss of water vapor from the leaf due to diffusion and evaporation. (1 pt)
[transpiration]
5. Division of the cytoplasm into 2 daughter cells. (1 pt)
[cytokinesis]
6. Alternate forms of a gene.(1 pt)
[alleles]
7. Small pore in a leaf that functions in gas exchange and to control water loss. (1 pt)
[stomata]
8. The exchange of corresponding segments between nonsister chromatids (1 pt)
[crossing over]
Answer the following questions.
9. Where are phosophodiester linkages found? (1 pt)
[Bond between the phosphate group and sugar in the DNA backbone]
10. What does nondisjunction result in?(1 pt)
[daughter cells with abnormal numbers of chromosomes]
11. C4 plants and CAM plants both require more energy to fix CO2 than C3 plants. List one part of the
process that requires the extra ATP in either a C4 or a CAM plant. (1 pt)
[Regenerating pyruvate to PEP in C4 cycle, active loading of malate into vacuole in CAM plants]
12. What is the chromosomal theory of inheritance?(1 pt)
[genes found on specific locations on chromosomes]
13. What is the function of cohesin proteins?(1 pt)
[Hold sister chromatids together at the centromere]
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Biol 211, Fall 2008
Exam #3
Name ____________________
14. At which end do kinetochore microtubules shorten in pig kidney cells; a) kinetochore attachment end
or b) pole end? (1 pt)
[kinetochore end]
15. What is one advantage asexual reproduction has over sexual reproduction? (1 pt)
[If parent well adapted, offspring well adapted / quicker / less energy]
16. What is an inversion? (1 pt)
[Piece of chromosome detached and reattached in reverse]
17. Name one protein involved in the separation of the DNA strands for replication and briefly give its
function. (1 pt)
[helicase – separates strand / single-stranded binding proteins – keep DNA from reconnecting /
topoisomerase – releases strain on DNA by cutting, unwinding and reattaching]
Section 2. Short Answer.
18. Provide a concise definition for each that will clearly distinguish between the following pairs of
terms. Be sure to include how the two terms are related to one another. (2 pts each):
a) C4 plants / CAM plants
Both are adaptations for plants living in warmer climates and need to avoid photorespiration. They do
this by having an alternative pathway to fix carbon so they can increase the concentration of carbon in
the Calvin cycle so that rubisco does not bind oxygen. Both use the C4 pathway of fixing carbon.
C4 plants open their stomata during the day, but can keep productivity high even when their stomata are
closed because they use PEP carboxylase to fix carbon initially and move that carbon in the form of
malate into the bundle sheath cells, where Calvin cycle occurs. Malate breaks down, provide CO2 for
the Calvin cycle. C4 plants use a spatial separation (two types of cells) of initial carbon fixation and
calvin cycle in order to keep CO2 levels high in Calvin cycle.
CAM plants use temporal separation of carbon fixation and Calvin cycle. They open their stomata only
at night and use the C4 pathway with PEP carboxylase to fix carbon into malic acid, which is stored in
the vacuole overnight. Malic acid is release in the daytime, where it can convert to CO2 & pyruvate to
supply the Calvin cycle with CO2. CAM plants do not have 2 different cell types for photosynthesis.
b) leading strand / lagging strand
Both are sections of the chromosome that are being replication.
Leading strand is the part of the strand that is being continuously replicated in the direction towards the
replication fork.
Lagging strand gets replicated discontinuously in small fragments (Okazaki fragments) and is replicated
in the direction away from the replication fork
c) pleiotrophy / polygenic inheritance
Both are types of inheritance patterns. Pleiotrophy is where one gene affects multiple phenotypes.
Polygenic inheritance is where one phenotype is affected by multiple genes.
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Biol 211, Fall 2008
Exam #3
Name ____________________
Answer the following questions.
19. What are telomeres and why are they necessary? (3 pts)
[repeating sections at the end of linear chromosomes. Non-coding. Chromosomes shorten with each
replication. Telomeres get shortened rather than genes. Also function to signal cell to go into
permanent non-dividing stage.]
20. a) Describe Mendel’s Law of Independent Assortment (MLIA). (2 pts)
[Traits assort independently]
b) Linked genes violate Mendel’s LIA. Under what circumstances might it appear that Mendel’s
LIA holds true for linked genes? (2 pts)
[traits found on the same chromosome travel together - do not assort independently. genes
located further apart are subject to crossing over, which make the traits travel independently]
21. Why are the most common lethal genetic disorders found in a population recessive traits rather than
dominant traits? (2 pts)
[An individual can be a carrier (Ll) of a lethal recessive allele, so the allele remains in population.
The dominant lethal allele will only remain in the population if it kills the individual after it reproduces.]
22. What would happen to a cell at the G2 checkpoint if the concentrations of cyclin failed to increase
during the S phase? (3 pts)
[Not enough to bind with cyclin dependent protein kinase, so no MPFs, so no going past G2
checkpoint into mitosis]
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Biol 211, Fall 2008
Exam #3
Name ____________________
23. The question of whether DNA or protein is the genetic material was the subject of much research
earlier in the 20th century. Briefly describe one experiment that provided evidence that DNA is the
genetic material. (3 pts)
[Must be an experiment that address the protein vs. DNA question. Frederick Griffith experiment with
did not directly address this question, just whether material (of some kind) can be transferred). Oswald
Avery built on Griffiths experiment, using a similar protocol. He tested DNA, RNA and proteins. He
inactivated all but one of the suspects in each treatment and was able to show that only when DNA was
activated did transformation occur. Alfred Henry & Martha Chase did the definitive experiment on this
question. They labeled both the DNA and the protein coat of a bacteriophage and allowed them to infect
a bacteria. The bacteria and bacteriophages were put in a blender to separate them. By examining the
radioactive labels they were able to determine that it was the DNA that went into the bacterial cells.]
24. a) What is the role of PEP Carboxylase in photosynthesis and why is it important? (3 pts)
[Attaches CO2 to PEP in C4 cycle (used by both C4 and CAM plants). Rubisco binds O2 when CO2
levels low. Provides way to increase amount of CO2 and decrease chance of photorespiration.]
b) Why is rubisco considered the most abundant enzyme on the planet? (2pts)
[Because rubisco also binds O2, plants compensate by increasing the number of enzymes to increase
likelihood of them binding to CO2]
25. A female Drosophila (fly) was crossed with a white-eyed male fly. The genotype of the male fly
was XwY (w = white eye allele that is recessive, w+= red-eye allele is dominant.) Half of the male and
half of the female offspring were red-eyed, and half of the male and half of the female offspring were
white-eyed. What was the genotype and the phenotype of the female fly? Show all of your work. (2 pts)
You are given the results (the inside of the Punnet square), so can then work backwards to find the
unknown parental genotype.
Male = XwY
Xw
Y
w
X
Xw Xw XwY
Xw+
Xw+Xw Xw+ Y
In order to get these ratios, the female must be Xw Xw+ and has red eyes.
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Biol 211, Fall 2008
Exam #3
Name ____________________
Bonus Question (2pts)
Answer only one of the question below.
1. What would happen, in terms of a cell’s ability to do photosynthesis, if a mutation occurred that
caused the primary electron acceptor in the water-splitting photosystem (PS2) to become a stronger
electron acceptor than the chlorophyll a in the NADPH-producing photosystem (PS1)? Be specific.
[Electrons would no longer be “pulled” down the ETC. So no H+ would be pumped across the ETC, so
no gradient, so no ATP produced. No ATP to go into the Calvin cycle, so no production of G3P. Also
no NADPH produced to go into the Calvin cycle.]
2. What are two ways that pyruvate dehydrogenase can be regulated?
[high ATP inhibits, low ADP stimulates, also needs coenzyme]
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