Cytogenetics Multiple Choice Questions 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
Clarification: 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.
2. What is the capacity of viral gene storage termed as?
A. Viral capacity
B. Tight head capacity
C. Head full capacity
D. Virulent capacity
Answer: C
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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
Clarification: 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