1. Lambda-ZAPII can carry what size of the foreign DNA?
a) 1 kb
b) 5 kb
c) 10 kb
d) 15 kb
Explanation: Lambda-ZAPII is a lambda insertion vector that can take up to 10 kb of foreign DNA into any one of 6 restriction sites within a polylinker, incorporated within the lacZ’ gene.
2. How can lambda-ZAPII recombinants be distinguished?
a) Agar + ampicillin plating
b) Agar + tetracycline plating
c) Plaque morphology analysis
d) Agar + X-gal plating
Explanation: Insertion of foreign DNA in the polylinker containing restriction sites leads to inactivation of the lacZ’ gene. Hence recombinants can be distinguished as white colonies from non-Recombinant blue colonies.
3. What is a “stuffer fragment” in cloning jargon?
a) A replaceable fragment
b) Promoter region
c) Ribosomal binding site
d) Clustered with restriction sites
Explanation: Stuffer fragment is a replaceable fragment flanked by two recognition sites for the restriction endonuclease. Often this fragment carries additional sites that can be used to cut it up into small pieces so that its own re-insertion is unlikely.
4. What is not true in regard to a lambda replacement vector?
a) It contains two/more restriction sites
b) Contains stuffer fragment
c) Recombinant selection by size
d) Carries smaller DNA than insertion vectors
Explanation: Replacement lambda vectors are designed to carry larger pieces of DNA than the insertion vectors and upto 20 kb is the capacity whereas that of an insertion vector is 10 kb.
5. How can recombinant selection for lambda replacement vectors be done?
a) In vitro packaging
b) cI gene inactivation
c) Lac selection
d) Antibiotic resistance
Explanation: The replacement vectors are created so as to carry larger pieces of foreign DNA ad hence size constraints are put for in vitro packaging to occur. Small DNA chunks hence will not pack into the phage head.
6. Lambda-EMBL4 is an example of _________
a) Insertion vector
b) Replacement vector
c) Hybrid vector
d) Mammalian vector
Explanation: It is a lambda replacement vector and can carry upto 20 kb of foreign DNA by replacing a segment flanked by EcoRI, BamHI and SalI restriction endonucleases sites.
7. Recombinant selection of lambda-EMBL4 can be done on the basis of Spi phenotype.
a) true
b) false
Explanation: Spi phenotype can be used to distinguish recombinants of the replacement vector from the non-recombinants. Sensitive to P2 phage infection: for phages that do not infect hosts if it is already infected by P2 phage.
8. What is a pre-requisite for cloning experiments with lambda insertion or replacement vectors?
a) Circular form of the vector
b) Small size
c) Helper phage integration
d) Two-phage system
Explanation: For a replacement or insertion vector to stably infect the host, it is required that the vector be in its circular form with cos sites hydrogen bonded to each other.
9. What are cosmid vectors?
a) Hybrid between phage and plasmid
b) Hybrid between M13 and lambda phage
c) Modified lambda vector
d) Modified M13 vector
Explanation: Cosmids are hybrid between lambda phage and bacterial plasmid. The construction of cosmids centers on the fact that only cos sites are required for packaging the DNA into a phage protein coat
10. What is the basis of cosmid construction?
a) Origin of replication is vital
b) Only cos sites are required for packaging
c) Promoter sequences for expression
d) Different restriction sites
Explanation: The design of a cosmid vector exploits the fact that only the cos sites are responsible for in vitro packaging of foreign DNA into phage protein coat.