Dr. Reichler’s Bio 301L   MWF 9-10am    Print Name:____________KEY_______________
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 introns.
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 blood clots.
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?  (8 pts)
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.
(8 pts)
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 codominance.  100%

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 pts)
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.