This set of Genetic Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Cre Lox Excision”.
1. The ________ protein of bacteriophage P1 mediates site-specific recombination at a 34 bp sequence, loxP.
a) cre recombinase
b) gene II
c) gene IV
d) gene VIII
View Answer
Explanation: The Cre recombinase protein of bacteriophage P1 mediates site-specific recombination at a 34 bp sequence, loxP.
2. Choose the incorrect statement for cre-lox excision.
a) The chromosomal copy of the target gene replaces the target gene flanked by loxP sites
b) The second step is supply of Cre recombinase
c) Integration of cre takes place under a controllable promoter followed by induction of the promoter
d) Induction results in expression of cre, recombination along loxP sites and excision of the sequence between
View Answer
Explanation: For cre-lox excision, the chromosomal copy of the target gene is replaced by target gene flanked by loxP sites. The second step is supply of cre recombinase. Integration of cre is done by a controllable promoter which is followed by the induction of promoter. This induction results in expression of cre and recombination along loxP sites, leading to excision.
3. Cre can be introduced by crossing it with a strain containing the gene or by infection with virus containing it.
a) True
b) False
View Answer
Explanation: Generally cre is introduced with the help of a promoter. But it can also be introduced by crossing it with a strain containing the gene or by infection with virus containing it.
4. How much effect is there on the surrounding genes by the loxP sequence which is left after recombination has taken place?
a) Little effect
b) No effect
c) Huge effect
d) It depends on the nature of the surrounding gene
View Answer
Explanation: As the recombination has taken place, the loxP sequence remains there. The remaining loxP sequence has no effect on the surrounding genes.
5. The ability to control the expression of cre allows controlling what?
a) recombination
b) replication
c) excision
d) packaging
View Answer
Explanation: The ability to control the expression of cre allows when and where excision takes place. Specific excision of the target takes place if an expression is tissue or time specific.
6. Excision of DNA flanked by loxP sequences is also known as _________
a) subtle excision
b) croxing
c) floxing
d) sequence specific excision
View Answer
Explanation: Excision of DNA flanked by loxP sequences is called as floxing at times. Other site specific recombination systems are also used.
7. RNA molecule with catalytic activity is termed as________
a) ribosomes
b) catalytic RNA
c) reactive RNA
d) ribozyme
View Answer
Explanation: Any RNA molecule with catalytic activity is termed as a ribozyme. Some of the catalytic activity can be removal of introns by self-splicing.
8. Hepatitis delta virus capable of self cleavage.
a) True
b) False
View Answer
Explanation: Hepatitis delta virus, which is associated with hepatitis B is capable of self cleavage. Ribozymes mainly comprise of RNA molecules which are capable of self cleavage.
9. Choose the correct statement for self cleavage reaction.
a) It is nucleophilic attack reaction by 2’ hydroxyl of RNA
b) It is nucleophilic attack reaction by 3’ hydroxyl of RNA
c) It is nucleophilic attack reaction by 2’ hydroxyl of DNA
d) It is nucleophilic attack reaction by 3’ hydroxyl of DNA
View Answer
Explanation: In the self cleavage reaction, it is an internal nucleophilic attack reaction by 2’ hydroxyl of RNA. The attack is done on the phosphate group in the sugar phosphate group.
10. Self cleavage reaction can take place in?
a) DNA
b) RNA
c) Both DNA and RNA
d) Can take place in both but is preferred in DNA
View Answer
Explanation: The self cleavage reaction takes place in RNA. It is because it involves a nucleophilic attack by 2’ hydroxyl, which is found in RNA and not in DNA.
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