1. What is the size of fragments that can be obtained by using a phagemid vector?
a) 1 kb
b) 10 kb
c) 1500 bp
d) 50 kb
Explanation: With a phagemid vector such as Pembl8, single-stranded versions of cloned DNA fragments up to 10 kb can be obtained, greatly extending the range of M13 cloning system.
2. What is the size limit for in vitro packaging of an unmodified lambda vector?
a) 10 kb
b) 52 kb
c) 100 kb
d) 10 bp
Explanation: The lambda DNA molecule can be increased in size by only 5%, representing the addition of only 3 kb of new DNA. If total size of the molecule id more than 52 kb, then it cannot be packaged.
3. Which non-essential region of the lambda phage can be deleted without impairing viability?
a) Protein coding
b) Promoter region
c) Integration and excision region
d) Terminator region
Explanation: The removal of non- essential region between 2 to 35 positions on the restriction map decreases the size of the vector by 15 kb and increasing its efficiency of carrying foreign DNA.
4. What is the basic difference between a modified (non-essential regions removed) and an unmodified lambda vector?
a) Gene expression increases
b) Stable infection
c) Non- lysogenic cycle
d) Star activity
Explanation: Since the non-essential region of the lambda genome which is responsible for integration into the host genome is removed, it no longer follows the lysogenic cycle hence goes infecting the cell and eventually losing them.
5. Why is natural selection used to isolate modified lambda that lacks certain restriction sites?
a) Strains that lack sites are known
b) Easier than in vitro mutagenesis
c) There are no restriction sites in lambda
d) Natural selection is less time consuming
Explanation: There are multiple recognition sites in a lambda phage and only mutant strains that contain not many of these sites can be used as cloning vectors. To get hold of such mutant strains a host E.Coli strain that produces EcoR1 is used.
6. Which of the following assertions is true in regard to a cosmid vector?
a) No plaques are produced
b) Lac-selection system is used
c) It can carry small DNA fragments
d) Origin of replication is taken from lambda
Explanation: The cosmid is a hybrid between lambda phage and a plasmid and only the cos sites in the whole construct of cosmid belong to the phage. Ampicillin and tetracycline resistance genes are taken from the plasmid, no plaque formation is observed.
7. Insertion and replacement vectors are modified vectors of which of the following?
a) Plasmid
b) Lambda phage
c) M13 phage
d) Yeast artificial chromosome
Explanation: Once the problems associated with lambda vector; packaging constraints and multiple restriction sites had been solved, development of different types of modified lambda vectors is done.
8. What type of vector is the lambda-gt10?
a) Insertion vector
b) Replacement vector
c) Hybrid vector
d) Unmodified lambda vector
Explanation: It is a vector which can carry up to 8 kb of new DNA, inserted into unique EcoR1 site located in the Ci gene. Recombinants are distinguished as clear plaques.
9. Which property is not associated with a lambda insertion vector?
a) Non-essential region removed
b) Two vector arms ligated together
c) At least one restriction site is present
d) Expression of the gene can be obtained
Explanation: Insertional lambda vectors are cloning vectors and not expression vectors because they do not contain promoter sequences and ribosomal binding sites and hence the expression of the inserted gene cannot be obtained.
10. How can identification of recombinants of lambda-gt10 vector be done?
a) Ampicillin resistance
b) Lac selection
c) cI gene insertional inactivation
d) Agar and X-gal plating
Explanation: The foreign DNA in this vector is cloned within the cI gene containing the EcoR1 restriction site. The recombinants hence are distinguished as clear plaques from the non-recombinant turbid plaques.