Dr. Reichler’s Bio 301L MWF 9-10am Print
Exam #2 October 24, 2005
Read each question carefully and don’t hesitate to
ask if a question seems unclear. If possible, answer each
question in the space provided, but if needed, continue on the
back. If you use a drawing as part of your answer, be sure to
also include a written explanation. These questions have specific
answers, although for some, more than one answer is possible. To
receive full credit you must clearly and fully answer the question
being asked. This exam is worth 103 points with the points for
each question noted in parentheses.
1. Different versions of Dscam proteins are made in different neurons,
but they are all coded for by the same gene. Could you express
two different versions of Dscam in a single bacterium? Why or why
not? (8 pts)
Either: No, Different versions
of Dscam arise from alternate splicing, and bacteria cannot remove
Yes, by putting two plasmids into the
same bacteria, with the different versions of Dscam produced via
reverse transcriptase from cells expressing the different versions, one
bacterium could express both versions.
2. If a gene was methylated, would acetylating the adjacent histones
allow the gene to be expressed? Why or why not? (4 pts)
No, methylation blocks transcription,
so even if it were unpackaged, it would not be expressed.
3. Fibrin is a protein involved in blood clotting. During blood
clotting, would the transcription of the fibrin gene change? Why
or why not? (8 pts)
Either: No, inactive fibrin
protein circulating in the blood, fibrinogen, is activated to form
Yes, the body will need to replace
the fibrinogen that was activated to make fibrin,
4. How is DNA polymerase important in protecting us from cancer?
It replaces incorrect nucleotides
that are incorporated during DNA replication, thereby reducing the
number of mutations.
5. The elimination of what protein would stop a cell from successfully
completing mitosis? Why would the elimination of this protein
stop mitosis? (8 pts)
Any one of: DNA polymerase,
helicase, primase, or ligase- if the cell cannot replicate its DNA, it
cannot enter mitosis. Histone- if cell cannot package DNA, it
cannot do mitosis.
6. Where in your body would you expect the telomerase gene to be
methylated, and where in your body would you expect the telomerase gene
to not be methylated? (8 pts)
Telomerase would be methylated in any
cells that are not making gametes. It would NOT be methylated in
cells producing gametes.
7. Why are malignant cancers more dangerous than benign cancers, and
what is one way that the treatment of malignant and benign cancers
would differ? (8 pts)
Malignant cancer cells have poor cell
adhesion. To treat a malignant cancer, chemotherapy must be used
to ensure that all cancer cells all over the body are eliminated.
8. Describe, by giving a name or function, one gene that would have its
adjacent histones acetylated and one that would not have its adjacent
histones acetylated in a cancer cell. Explain.
Acetyl;ation leads to DNA unpackaging
that is necessary for gene expression. Deacetylation leads to
tighter DNA packaging stopping gene expression.
Any one of:
Acetylated: positive cell cycle
regulators- induce cell division, telomerase- to keep telomeres from
getting too short, MDR- to export toxins, angiogenesis proteins- to
attract blood supply, DNA polymerase or any protein involved in DNA
replication- cell needs to replicate DNA prior to mitosis.
Not acetylated: negative cell cycle
regulators- allow cell to continually divide, DNA repair enzymes-
cancer cells have many mutations often caused by poor DNA repair.
9. Why does a cell’s risk of becoming cancerous increase as its
telomeres get shorter? (4 pts)
Shorter telomeres is indicative of
many DNA replications, and each DNA replication leads to more
mutations, with each mutation the risk of cancer increases.
10. Chimpanzees have 24 pairs of chromosomes while humans have 23 pairs
of chromosomes. Based on this, which species would have more
genetic diversity? Why? (4 pts)
Chimps, more chromosomes means more
genetic diversity due to independent/random assortment.
11. In vampires fang length is controlled by one gene with two alleles
(L= long and S=short fangs). A vampire with long fangs and a
vampire with short fangs have an offspring with medium length
fangs. How can this be explained? What is the chance that
their next offspring will have medium length fangs? (Show your
work to receive partial credit.) (8 pts)
Incomplete dominance OR
12. In Vampires sex determination works as it does in humans. On
the X chromosome is the gene coding for resistance to garlic, (G =
sensitive (dominant); g = resistant (recessive)). Joe a garlic
resistant vampire mates with Julia who is garlic sensitive, but her
father was resistant. Julia is pregnant with a girl and a
boy. What are the chances of the girl being sensitive to
garlic? What are the chances of the boy being sensitive to
garlic? (Show your work to receive partial credit.) (8 pts)
Girl= 50% Boy= 50%
13. When and why is ligase used during genetic engineering? (8
Once the gene of interest and the
plasmid have been cut by restriction enzymes and placed together, they
make ionic bonds from the sticky ends…ligase makes covalent bonds to
permanently insert the gene of interest into the plasmid.
14. What two characteristics about how restriction enzymes cut DNA are
critical for their use in genetic engineering? (8 pts)
They cut at only specific DNA
sequences, and they leave sticky end overhangs.
Bonus: How did
researchers get people to ignore an individual’s race, and using these
experiments what did they propose about racism? (3 pts)
By giving other clues as to group
membership, such as team affiliation, etc. They proposed that
racism is not an inherited or innate trait, but that identifying people
by their “tribe” is.