Dr. Reichler’s Bio 212  MW10-11am    Print Name:_______KEY_____________
Exam #3   April 9, 2003

    Answer each question as succinctly as possible in the space provided.  If needed, continue on the back.  If you use a drawing as part of your answer, be sure to also include a written explanation.  Read each question carefully and don’t hesitate to ask if a question seems unclear.  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.  Each question is worth 6 pts, unless otherwise noted, for a total of 100 points possible for this exam.

1. a.  You want to produce giant pumpkins for Halloween.  Would you use genetic engineering or breeding (artificial selection)?  Explain.
Genetic Eng- can rapidly pick genes and insert them into the pumpkins.  With inserting genes can make larger than natural pumpkins.
Breeding- may take longer, but can choose largest pumpkins and breed them.  Will only get pumpkins as big as largest natural ones.

b. Describe the function of three enzymes that would be used in the genetic engineering of a human gene into bacteria?  Number the three enzymes in the order that they would be used.  (8pts)
Any three of:  1. Reverse transcriptase- to make cDNA from mRNA, 2. DNA polymerase- to amplify the DNA by PCR, 3. Restriction enzymes- to cut the DNA/plasmid, 4. ligase- to make covalent bonds between the inserted gene and plasmid
(2 pts each enzyme, 2 pts for correct order)

c. How would you know whether the genetic engineering of a human gene into bacteria had been successful?
Selection.  Grow bacteria in presence of antibiotic, only bacteria containing plasmid with antibiotic resistance gene will survive.

d. How do cycles of heating and cooling allow the Polymerase Chain Reaction (PCR) to occur?
Heating separates the DNA strands, Cooling allows the primers to bind so that DNA polymerase can copy the DNA.

e. You want to produce a cDNA for human telomerase.  What do you need from humans to produce this cDNA, and what cells would you use as your source material?
mRNA for telomerase.  Can get it from rapidly dividing cells like shin or stomach lining, cancer, or from gametes.

2. a.  How are the cells that result from mitosis genetically different from each other?
DNA replication can cause some mutations that will make the DNA slightly different.

b. If a cell cannot replicate its DNA, what part of the cell cycle is it stuck in?  (4pts)
G1 or G0, it cannot enter S

c. What triggers the separation of sister chromatids during mitosis?
Chromosomes lining up at middle of cell.  Known as metaphase checkpoint (M checkpoint)

3. a.  Would a mutation that causes non-functional cyclin lead to cancer?  Why or why not?
No, Cyclin is a positive signal, and the cell would not be able to enter mitosis, or continue mitosis, without this positive signal.
3/6 pts for saying that needs multiple mutations to cause cancer.

b. How would knowledge about gene expression in a tumor help in the treatment of cancer?
If they are over-expressing MDR, then they will be resistant to chemotherapy.  OR  tumors not expression or poorly expressing genes that hold the cells together are likely to be malignant.

c. In real practice multiple cancer treatments are commonly used concurrently.  After surgery to remove a tumor, what other treatment would be used?  Explain.
Chemotherapy- to kill any remaining cancer cells.

d. How do telomeres help prevent cancer?
Telomeres limit the number of cell divisions thereby limiting the number of mutations by replication errors.

4. a.  What is similar and what is different between the chromosomes in a homologous pair?
They have the same genes, but different versions (alleles).

b. Where does meiosis occur in humans?  (4pts)

c. During meiosis, which occurs first, crossing-over or independent assortment?  Explain.
First crossing-over occurs as the chromosomes package (prophase), then ind assort occurs as chrom line up in middle (metaphase)

5. Identical twins are genetically identical siblings.
a. Why is this unusual?
Each gamete is unique, in humans trillions of possible combinations, so having two fertilizations of genetically identical gametes is incredibly rare.

b. How might genetically identical siblings be formed?
The zygote splits into two, forming identical fetuses.