Microbiology Multiple Choice Questions on “Bacterial Conjugation”.
1. The first demonstration of recombination in bacteria was achieved by _______________
A. Lederberg and Tatum
B. Luria and Delbruck
C. Joshua and Lederberg
D. Luria and Tatum
Answer: A
Clarification: The first demonstration of recombination in bacteria was achieved by Lederberg and Tatum in 1946 in a brilliant and remarkable experiment that opened the door to a whole new world of microbiology.
2. Mating between species is necessary for recombination to take place.
A. True
B. False
Answer: A
Clarification: In a regular cycle of sexual reproduction, there is an opportunity for different mutants of a species to mate with each other and produce new individuals with new combinations of mutations, i.e., to produce recombinants.
3. Which type of E.coli strain was chosen to prove the experiment of conjugation?
A. prototrophs
B. auxotrophs
C. polyauxotrophs
D. autotrophs
Answer: C
Clarification: When Lederberg and Tatum did their experiments, they used polyauxotrophs (mutants with more than one nutritional requirement) so that back mutation to the wild type does not occur.
4. In conjugation only small fragments of the bacterial chromosome are transferred.
A. True
B. False
Answer: B
Clarification: In conjugation it is possible for large segments of the chromosome, and in special cases the entire chromosome to be transferred.
5. What is the shape of DNA in the male cells of E.coli?
A. linear
B. supercoiled
C. circular
D. relaxed
Answer: C
Clarification: Male cells contain a small circular piece of DNA, which is in the cytoplasm and not part of a chromosome.
6. Which of the following cells of E.coli are referred to as F—
A. Male cells
B. Female cells
C. Both male and female cells
D. Neither male nor female cells
Answer: B
Clarification: Female cells lack the sex factor or F factor (fertility factor) and are labeled as F—. They are recipient cells.
7. What is the frequency of formation of recombinants in a F+ X F— cross?
A. 100
B. 40
C. 10
D. 1
Answer: D
Clarification: The formation of recombinants in a F+ X F— cross occurs at a low frequency— about one recombinant per 104 to 105 cells.
8. The F factor DNA is sufficient to specify how many genes?
A. 2
B. 10
C. 40
D. 100
Answer: C
Clarification: The F factor DNA is only sufficient to specify about 40 genes that control sex-factor replication and synthesis of sex pili.
9. Which of the following is true for an Hfr X F— cross?
A. frequency of recombination high, transfer of F factor low
B. frequency of recombination high, transfer of F factor high
C. frequency of recombination low, transfer of F factor high
D. frequency of recombination low, transfer of F factor low
Answer: A
Clarification: In an Hfr X F— cross, the frequency of recombination is high and the transfer of F factor is low as here the F factor of the Hfr is rarely transferred during recombination.
10. Which of the following can be used as a measure to construct a linkage map of the Hfr chromosome?
A. frequency of recombination
B. time of entry
C. locus of mutation
D. transfer of F factor
Answer: B
Clarification: Each gene enters the F— cell at a characteristic time, and a linkage map of the Hfr chromosome can be constructed using time of entry as a measure.
11. The Hfr chromosome is transferred to the F— cell in a _____________ fashion.
A. circular
B. coiled
C. dimer
D. linear
Answer: D
Clarification: The Hfr chromosome is transferred to the F— cell in a linear fashion even though it is a circular chromosome.
12. How much time is required to inject a copy of the whole Hfr E.coli genome?
A. 24 hrs
B. 30 mins
C. 100 mins
D. 48 hrs
Answer: C
Clarification: It takes about 100 min to inject a copy of the whole Hfr E.coli genome (i.e., the chromosome and the integrated F factor.
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