Cytogenetics Questions and Answers – Gene Mapping in Bacteria by Transduction

This set of Cytogenetics Multiple Choice Questions & Answers (MCQs) focuses on “Gene Mapping in Bacteria by Transduction”.

1. Which of the following viruses will be useful for transduction?
a) T2 phage
b) T4 phage
c) T7 phage
d) Lamda phage

Answer: d
Explanation: T phages mainly undergo lytic cell cycle, while lamda phages have lysogenic cell cycle. For transduction to occur, the viral genome must integrate within the nucleoid else it will never incorporate bacterial gene within itself. Thus, only lamda phage will be able to help in transduction.

Answer: c
Explanation: The viral head has a specific capacity to load Nucleic acid. This capacity can be satisfied by only viral genome, a combination of viral and bacterial genome or only bacterial genome. This is called head full capacity.

3. In a transduction experiment where the recipient is Met-, Ala-, Gal- you observe a recombinant phenotype Met+, Gal+ in some strains and Gal+ Ala+ in some strains. But in none of the cases can you find Met+ Ala+. What is the sequence of the gene?
a) Met, Ala, Gal
b) Met, Gal, Ala
c) Gal, Met, Ala
d) Gal, Ala, Met

Answer: b
Explanation: The recombinant genotype Met+ Ala+ will only result in the case when there is a double cross over such that the middle portion is exchanged twice. This is of least occurrence and is deterministic for the sequence.

4. You are checking the sequence of 3 genes using generalized transduction mapping. The recipient is Leu-, AziS, Thr- while the donor is Leu+, AziR, Thr +. If you select the Leu+ as marker, AziR would be 50% while Thr+ would be 2%. If you select Thr+ as marker Leu+ would be 3% and AziR would be 0%. What is the sequence?
a) Thr Leu Azi
b) Azi Thr Leu
c) Azi Leu Thr
d) Thr Azi Leu

Answer: a
Explanation: Genes Leu and Azi and genes Leu and Thr have a tendency to be incorporated together; this is as a result of their physical proximity. On the other hand Thr and azi hardy show such tendency so they must be farther apart. This results in the sequence with Leu in the middle.

5. Which of the following is not true for specialized transduction?
a) The lysogenic viruses can perform this
b) A variety of genes can be transformed in this case
c) The viral genome is then incorporated in the bacterial genome
d) It is seen in lamda phage like K12

Answer: b
Explanation: Here the viral genome is actually incorporated in the bacterial genome at a particular site. The virus can transfer the gene surrounding its recombination site only. It is certainly through lusogenic cycle which is seen in lamda phages including K12.

6. The Phage is incorporated in the bacterial genome by _____________________
a) Single crossover event
b) Two crossover event
c) Three point recombination
d) 4 crossover event

Answer: a
Explanation: A viral genome is introduced in bacteria as a circular plasmid. It will be incorporated by a single cross over between the att site of virus and the att Lamda site of bacteria.

7. Which of these is correct according to transduction?
a) Specialized transduction is due to excision error
b) F’ plasmid can act in specialized transduction
c) Only specialized transduction in virus can be used to cause genetic variations
d) Bacteriophage nucleic acid is dispensable for virulence

Answer: a
Explanation: When the Lysigenic virus enters Lytic cycle its gene has to excise out of the bacterial genome. Imperfections in this excision can cause excision of a part of bacterial genome along with the circular viral genes. This results in specialized transduction.

8. If the bacterial DNA sequence is Leu Met Att Gal Bio, which of the genes can be transferred via specialized transduction?
a) Leu and Met
b) Met, Att and Gal
c) Gal and Bio
d) Met and Gal only

Answer: d
Explanation: Att site is merely necessary for incorporation of the virus. In specialized transduction the sites directly beside the attachment point of the virus can be mistakenly excised with the part of viral gene. Here this phenomenon will occur only in case of Met and Gal.

9. A specialized transducing virus attacks a healthy bacterial cell. What will be the virulence of the viruses produced by this bacterial cell after infection?
a) They will me more virulent than original one
b) They will be equally virulent as original one
c) The virulence will depreciate
d) No virulence

Answer: d
Explanation: This is because some part of the viral genome is compromised for this improper excision making it specialized transducing phage. Without the complete viral genome, the resultant viruses will not be able to express their infective activity.

10. In which of the following cases will the viral progeny generated retain their infection ability?
a) A generalized trasducing phage affects a normal cell
b) A specialized transducing phage affects a cell infected by same virus
c) A specialized transducing phage will attack a normal cell
d) A generalized transducing phage will affect a cell with a different viral infection

Answer: b
Explanation: When the recipient is already infected by the same virus the complete genome of specialized tranducing phage is already present. This will produce normal infective virus as well as more specialized transducing infective viruses.

11. A specialized transducing phage attacking an infected cell with lysogenic stage of the same virus gives rise to________
a) HFR
b) HFT
c) F’
d) F

Answer: b
Explanation: Hft or High frequency transducing viruses has a greater tendency to produce specialized transducing phage by improper excision event as they are very unstable. HFR occurs by integration of F plasmid after conjugation.

12. The recombination study of phages is done using ____________
a) OD measurement
b) Plaque assay
c) Plating assay
d) Boyden chamber assay

Answer: b
Explanation: In Plaque assay bacterial culture is grown in a plate and then it is infected by the viruses. The plaque so formed by the viruses is studies to categorize the morphological features and study the recombination.

Sanfoundry Global Education & Learning Series – Cytogenetics.

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