Vector Biology Multiple Choice Questions on “Identification of Recombinants”.
1. Which of the following refers to the inactivation of Insertional inactivation?
A. Host
B. Gene of Interest
C. Gene of the vector
D. Gene of the host
Answer: C
Clarification: The incorporation of a DNA fragment into the vector leads to inactivation of one more genes present on its genome and a characteristic coded by the inactivated gene will no longer be displayed by the host cells.
2. BamHI cuts the Pbr322 at just one position, within the cluster of genes that code for resistance to ___________
A. Tetracycline
B. Ampicillin
C. Kanamycin
D. Gentamycin
Answer: A
Clarification: Pbr322 carries genes that code for tetracycline resistance. When cleavage of the molecule is done using endonuclease to insert a DNA fragment, the tetracycline genes are deactivated and the resistance is lost.
3. On a medium containing ampicillin, when pBR322 recombinants were plated. Which of the following will not be able to grow?
A. pBR322 containing gene of interest
B. self-ligated Pbr22
C. non-transformants
D. transformed cells
Answer: C
Clarification: All transformed cells that are those which took up the plasmid will grow on the ampicillin plates because only tetracycline resistance gene is inactivated.
4. Which of the following techniques is used in recombinant identification?
A. Ligation
B. Isolation
C. Replica plating
D. Restriction digestion
Answer: C
Clarification: Recombinants are first plated onto an agar plate containing antibiotic, for further screening replica plating of previously grown colonies is done to check growth on second antibiotic containing plate.
5. lacZ’ gene present in a Puc series plasmid codes for which of the enzyme?
A. Beta-galactosidase
B. Lactase
C. Amylase
D. Nuclease
Answer: A
Clarification: lacZ’ gene codes for beta-galactosidase enzyme and cloning with a plasmid that contains this gene leads to insertional inactivation of the gene and recombinants are identified because of their inability to synthesize the enzyme.
6. Beta-galactosidase is one of a series of enzymes involved in the breakdown of lactose to glucose plus galactose. It is normally coded by the gene lacZ, which resides on the E.Coli chromosome.
A. True
B. False
Answer: A
Clarification: The lacZ gene is encoded by the E.coli genome but some strains have modified lacZ gene and they can only synthesize beta-galactosidase enzyme when they harbor a plasmid that contains the missing element of the gene.
7. In screening for Puc8 recombinants, which color colonies will be the desired recombinants?
A. Blue
B. Colorless
C. White
D. Yellowish
Answer: C
Clarification: The Puc8 recombinants will have a non-functional lacZ’ gene due to insertional inactivation hence they will not metabolize X-gal and white colonies will result.
8. What is the compound X-gal?
A. Plasmid
B. Lactose analog
C. Antibiotic
D. Inducer
Answer: B
Clarification: X-gal is a lactose analog which is broken down by enzyme beta-galactosidase to give a product deep blue in color.
9. What is isopropylthiogalactoside?
A. Plasmid of pUC series
B. E.coli strain
C. Antibiotic
D. Inducer
Answer: D
Clarification: IPTG is an inducer of the enzyme beta-galactosidase. Along with X-gal, ampicillin and agar, IPTG is added to induce the enzyme and to perform screening for Puc recombinants.
10. Which of the following selection step does not occur in lac selection system?
A. Ampicillin resistance
B. X-gal plating
C. Agar plating
D. Replica plating
Answer: D
Clarification: In a lac selection system, both ampicillin and presence of beta-galactosidase are tested for on a single agar plate and replica plating is not required.