This set of Genetic Engineering Mcqs focuses on “Cloning in Lambda – 2”.
1. What happens if chain-termination mutation is in the S gene?
a) Cell lysis is blocked
b) Growth of cells containing low levels of packaging proteins is not allowed
c) The lysis of cells is not carried artificially
d) Packaging is not carried out efficiently
View Answer
Explanation: If chain-termination mutation is carried out is in the S gene, cell lysis is blocked. The growth of cells having high levels of packaging proteins is carried out. The lysis is then carried out artificially.
2. Which of the following is used for blocking the phage-encoded recombination?
a) Mutation in D gene
b) Mutation in E gene
c) Red mutation
d) Mutation in S gene
View Answer
Explanation: Red mutation is used for blocking the phage-encoded recombination. It ensures that no recombination or rearrangement takes place while carrying out packaging in vitro.
3. Which of the following is not a consequence of deletion in the b region?
a) Excision of the prophage on induction is prevented
b) It reduces the amount of endogenous phage DNA in the packaging mix
c) It reduces the amount of exogenous phage DNA in the packaging mix
d) It reduces the level of background non-recombinant phage
View Answer
Explanation: The deletion in the b region is responsible for preventing the excision of the prophage on induction. It reduces the amount of endogenous phage DNA in the packaging mix and thus resultantly it reduces the level of background non-recombinant phage.
4. If a single system is used for packaging, there are increased chances of endogenous material being packed.
a) True
b) False
View Answer
Explanation: In the case, if a single strain is used for packaging, there are increased chances of endogenous material being packed. It can be avoided by using additional mutations such as xis in the prophage to stop the excision and packaging of the lysogenic phage from the cells producing packaging extract.
5. The cI function can be scanned in order to check whether the recombinants are present or not. Which of the following doesn’t hold true?
a) The cI protein is required for the formation of lysogen
b) The plaques formed are turbid in the case if the cI gene is active
c) The plaques formed are clear in the case if the cI gene is inactive
d) hflA mutant host reduces the amount of cII stability
View Answer
Explanation: The cI protein is required for the formation of lysogen to take place. The plaques formed are clear in the case if cI is inactive and turbid in the case if cI is active. hflA (high frequency of lysogenization) mutant hosts is used for enhanced screening. It is so because it increases the amount of cII stability and thus consequently lysogenization is taking place efficiently.
6. What is the function of red and gam gene products?
a) It promotes the growth of the phage in the E. coli cells which are lysogenic for bacteriophage P1
b) It inhibits the growth of the phage in the E. coli cells which are lysogenic for bacteriophage P2
c) It inhibits the growth of the phage in the E. coli cells which are lytic for bacteriophage P1
d) It activates the growth of the phage in the E. coli cells which are lytic for bacteriophage P2
View Answer
Explanation: The red and gam gene products inhibit the growth of the phage in the E.coli cells which are lysogenic for bacteriophage P2. When red and gam gene products are absent, the growth takes place in the cells which are lysogenic to bacteriophage P2.
7. The red and gam genes are removed in which type of phages?
a) Substitution phage
b) Replacement and substitution phages both
c) Replacement phage
d) Substitution is preferred over replacement phage
View Answer
Explanation: The red and gam genes are removed in replacement vectors. And this can be used as a potent method to select the recombinants by plating them on P2 lysogen.
8. Phages which are designated as spi-are __________
a) red+ gam+
b) red+ gam-
c) red- gam+
d) red- gam-
View Answer
Explanation: red- gam- are called as spi- and they are not able to grow on P2 lysogens. The red+ gam+ mutants are called as spi+.
9. Choose the correct statement for RecBCD nuclease.
a) It promotes rolling circle replication
b) It is blocked by Gam protein
c) It blocks theta mode of replication
d) It is blocked by Red protein
View Answer
Explanation: RecBCD nuclease is blocked by Gam protein and it blocks rolling circle replication. As the rolling circle mode is blocked, replication would be carried out by only theta mode of replication.
10. The essential sites for recombination are known as __________
a) chi sites
b) rec sites
c) gam sites
d) red sites
View Answer
Explanation: The sites necessary for recombination are known as chi sites. Host recombination enzymes may not work until and unless the recombination sites are present.
11. The replication rate remains the same for all the phages irrespective of what sequence is there in the phage.
a) True
b) False
View Answer
Explanation: The replication rate is not the same for all the phages. Some phages having a certain insert may be replicating in a slower rate than that of other phages. Thus, there might be under-representation of some of the sequences.
12. There is a limit on upper size of the DNA to be packed. Choose the correct statement with respect to phages in this context.
a) There is some phage DNA lost in this process
b) The phages are known as transformed phages
c) These type of phages can’t be selected and harvested
d) Lambda is not a special attachment site
View Answer
Explanation: There is a limit on the upper size of the DNA to be packed. If the significant amount of sequence is flanked by the phage particles, there are chances of losing some phage DNA. These phages are known as transducing phages and can be easily selected and harvested for the lost DNA. Lambda is having a special site for attachment in E. coli.
13. There are some phages which don’t preferentially transduce some special regions of the phage genome. These phages are known as __________
a) transducing phages
b) specialized transducing phages
c) generalized transducing phages
d) transforming phages
View Answer
Explanation: Some phages are there which don’t preferentially transduce some special regions of the phage genome and they are known as generalized transducing phages.
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