1. A strain of Neurospora, unable to synthesize the vitamin thiamine (t) is crossed to a strain unable to synthesize the amino acid arginine (a).
Spore genotypes
No. of Asci
37 ++ ++ at at
33 +t +t a+ a+
34 at at ++ ++
36 a+ a+ +t +t
What information can be derived from these results for use in mapping these two loci? (Hint: linkage relationship and centromere distance).
2. The cross (abc) x (+++) is made in yeast. From the analysis of 100 asci, determine the linkage relationship between these 3 loci.
Spore genotypes
No. of asci
40 abc abc +++ +++
42 ab+ ab+ ++c ++c
10 a+c ++c ab+ +b+
8 a++ +++ abc +bc
3. Match the enzymes given below with the aspects of DNA below. More than one item may match some of the enzymes, so an item may be used more than once.
A. DNA gyrase
B. DNA ligase
C. DNA polymerase I
D. DNA polymerase II
E. DNA polymerase III
F. Primase
G. Helicase
H. Telomerase
a. extends DNA chains in a 5' to 3' direction
b. 5' to 3' exonuclease activity
c. The primary enzyme of DNA replication
d. Assembles RNA is a 5' to 3' direction
e. Needs a primer and a template to act
f. hydrolyzes ATP to unwind DNA
g. is main enzyme in removing RNA primer
h. is needed to join Okazaki fragments
i. Needs a primer, but not a template to act
j. a proofreading enzyme
k. nicks a DNA strad in front of a fork
4. The two chains composing a DNA double helix unwind, and a replication fork is formed. Chain A is presented to the DNA polymerase in the direction 3' - 5'. Its complementary chain, chain B, is presented in the direction 5' - 3'. Answer the following.
A. On which of the two chains will DNA synthesis occur in a direction toward the fork?
B. On which chain will the free -OH ends of replicating DNA be oriented toward the fork?
C. On which chain will the PO3 end of the RNA primer be directed toward the fork?
D. On which chain will the Okazaki fragments have -OH ends directed away from the fork?
5. Suppose that DNA did not replicate semiconservatively, as proposed by Watson and Crick. Assume that the double helox stays intact and a double helix composed of two new strands is formed at replication. This would be conservative rather than semiconser
vative replication. If DNA replication were conservative, what would have been the observations in the density gradient experiment of Meselson and Stahl?
6. You have isolated a new disease causing organism, and have extracted the genetic material. The organism contained nucleic acid with a remarkable base composition. A=21%, C=29%, G=29% U=21%. When heated it showed a major hyperchromic effect, and when k inetics were studied the nucleic acid of the organism exhibited the Cot curve shown below. est to isolate a disease causing organism was successfulOctober181995 (The complexity of T4 DNA is 105 base pairs). Analyze this information carefully and draw all possible conclusions about the genetic material of this organism, based on the above observations. What information is missing and needed to confirm your hypothesis about the nature of this molecule.
7. Draw out all possible base pairing combinations of Guanine (include both keto and enol forms).
8. Describe how the RAD9 gene was discovered. What is its significance to our understanding cell cycle control and cancer?
9. How does the mismatch repair system distinguish which strand to use as the template, and which strand to repair.
10. Following is a segment of DNA containing a palindrome.
A restriction enzyme that recognizes this produces breaks four nucleotides apart from the axis of symmetry is each strand. The break is to the left on the top strand, and to the right on the lower strand. Show the fragments that can be generated with comp lementary single-strand projections.
11. Following is a segment of circular plasmid:
A restriction enzyme specific for the palindrome present produces breaks four nucleotides apart from the axis of symmetry, to the left on the upper strand and to the right on the lower strand.
A. Show the ends that can be generated
B. Could the fragments generated is Ques. 10 be inserted? Explain your answer.
12. Compare and contrast classical versus reverse genetics.
13. What features are essential in a bacterial cloning vector; a eukaryotic shuttle vector?
14. Assume a certain nucleotide sequence is known to occur in the DNA of a rat. Chromatin is extracted from cells of different tissues and then exposed to a nuclease treatment that digests away the linker DNA, leaving the nucleosome cores. When the nucl eosome cores derived from chromatin of pancreas cells are subjected to further analysis, it is found that the particular sequence can always be recovered. However when chromatin taken from cells of the skin, liver and other sites is treated in the same w ay, the same DNA sequence is found to be lost, recovered only in part, or recovered at times in its entirety. Explain these findings.
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