MCB421 Exam 2: Photosynthesis, Bacteriophage Growth, Recombination, Bacterial Restrictions, Exams of Genetics

Download MCB421 Exam 2: Photosynthesis, Bacteriophage Growth, Recombination, Bacterial Restrictions and more Exams Genetics in PDF only on Docsity!

MCB

FALL 2005

EXAM 2

 PLEASE WRITE CLEARLY

 PUT YOUR NAME ON EACH PAGE

1. (12) There is a group of genes, A through F, mutations in which affect photosynthesis.

To see possible pathways within the group, you run epistatic analysis. The results

are as follows (the values are “deficiency factors”, derived by dividing the value

obtained for WT cells by the values obtained for the corresponding mutant):

WT A B C D E F G

WT 1

A 10 10

B 10 1000 10

C 10 10 1000 10

D 1000 1000 1000 1000 1000

E 10 1000 10 1000 1000 10

F 10 10 1000 10 1000 1000 10

G 10 1000 10 1000 1000 10 1000 10

How many pathways are there that affect photosynthesis? Are they dependent

upon a single gene?

3. (10) Consider a region of chromosomal DNA that contains 1000bp repeated sequences.

In one case, the sequences are orientated as direct repeats as shown in Figure 1 below.

Figure 1:

In the second case, they are orientated as inverted repeats as shown in Figure 2 below.

Figure 2:

For each construct, draw the products of a homologous recombination event between the

segments of homology. Be sure your diagram is very explicit in showing the

recombinants.

Extra space to answer question #3:

5. (12) Hughes and Roth did three factor crosses to confirm the order of the nadD gene

relative to the adjacent genes. What is the order of the lip , nad , and leuS genes?

[For each of the crosses in the table, show a drawing with the relevant

crossovers and the inferred gene order.]

Donor strain nadD

lip

leuS

Recipient strain nadD lip leuS

Selected

phenotype

Recombinants Number

obtained

Lip

nadD

+ leuS 100

nadD

leuS

nadD leuS 3

nadD leuS

NadD

lip

+ leuS 90

lip

leuS

lip leuS 100

lip leuS

6. (12) The proA , proB , and proC genes are required for the biosynthesis of proline.

You have a Str

S donor strain with a Hfr integrated between the proA

proB

and proC

genes as shown below.

proB

proA

proC

a. Given the same donor strain and a proC recA

+ Str

R recipient strain, how could

you isolate an F' proC

? [What medium would you use? How would you do

the experiment? Explain the rationale for the isolation scheme you would use.]

b. Draw a diagram showing how the F' proB

would form from this Hfr.

8. (8) It is possible to "cure" a strain of the plasmid pLAFR which encodes resistance to

tetracycline (Tet

R ) by mating in a second plasmid pPH1JI which encodes resistance to

gentamycin (Gen

R ).

a. What does this suggest about the properties of these two plasmids?

b. Would this trick work if the only selectable marker on pPH1JI was Tet

R ? Briefly

explain.

9. (10) ColE1 plasmids replicate in enteric bacteria but cannot replicate in Halobacterium

salinarium. The bop gene from H. salinarium was cloned into a ColE1 plasmid, and an

insertion mutation constructed that disrupted the plasmid encoded bop gene (indicated by

bop'-'bop in the figure below). This plasmid was then transformed into H. salinarium

with selection for resistance to the antibiotic mevinolin (Mev

R ).

a. The plasmid does not have any functional replication origin and, except for the bop

gene, the plasmid lacks any homology with the H. salinarium chromosome. How do

the Mev

R transformants arise? Show a diagram and briefly explain your answer.