Q110. Which enzyme creates DNA using RNA as its template?
[UPPCS — Practice]
- (a) Restriction enzyme
- (b) Reverse transcriptase
- (c) DNA ligase
- (d) Lipase
Answer: (b) Reverse transcriptase
Explanation: Reverse transcriptase copies RNA into complementary DNA. It is naturally associated with retroviruses and is widely employed in molecular diagnostics and cDNA synthesis. Researchers often combine reverse transcription with PCR when measuring RNA expression.
Q109. Consider recombinant-vector vaccines:
1. Genetic engineering is used in their design.
2. Certain viruses and bacteria serve as gene-delivery vectors.
Which statements are correct?
[UPSC CSE (Pre) 2021]
- (a) Both 1 and 2
- (b) 1 only
- (c) Neither statement
- (d) 2 only
Answer: (a) Both 1 and 2
Explanation: Recombinant-vector vaccines employ a modified virus or bacterium to carry genetic instructions for producing an antigen. Creating that construct requires recombinant DNA methods. Depending on the vector and antigen, these vaccines can stimulate antibody and cellular immune responses.
Q108. What does the term “metagenomics” most closely mean?
[RAS / RPSC — Practice]
- (a) Examining only one pure bacterial isolate
- (b) Measuring atmospheric temperature
- (c) Counting chromosomes through a microscope
- (d) Studying genetic material recovered directly from mixed environmental communities
Answer: (d) Studying genetic material recovered directly from mixed environmental communities
Explanation: Metagenomics analyses DNA or other genetic information from mixtures of organisms in environmental or clinical samples. It can reveal microbes that are difficult to culture, describe community diversity and identify metabolic capabilities from sequence data.
Q107. The Cas9 protein functions mainly as a:
[SSC CGL — Practice]
- (a) Plant hormone
- (b) Starch storage molecule
- (c) RNA-guided DNA-cutting enzyme
- (d) Structural protein of haemoglobin
Answer: (c) RNA-guided DNA-cutting enzyme
Explanation: Cas9 is a nuclease that makes DNA breaks at target sequences specified by guide RNA, subject to suitable PAM recognition. Cellular repair pathways then create the final editing outcome. It is one of several enzymes used in CRISPR-based systems.
Q106. What provides target-sequence recognition in standard CRISPR-Cas9 editing?
[SSC CHSL — Practice]
- (a) Ribosomal protein alone
- (b) Guide RNA
- (c) Insulin hormone
- (d) Chlorophyll
Answer: (b) Guide RNA
Explanation: A guide RNA contains a segment complementary to a chosen DNA target and directs Cas9 there. The enzyme also requires an appropriate PAM near the target. Changing the guide sequence can redirect the system to different genomic sites.
Q105. Which statements about mitochondrial replacement therapy are correct?
1. It may be performed before or after fertilisation.
2. Mitochondrial DNA is ordinarily transmitted maternally.
[UPSC CSE (Pre) 2021]
- (a) Both 1 and 2
- (b) 2 only
- (c) Neither 1 nor 2
- (d) 1 only
Answer: (a) Both 1 and 2
Explanation: Maternal spindle transfer occurs before fertilisation, whereas pronuclear transfer occurs after fertilisation. Both seek to reduce transmission of harmful maternal mitochondrial variants. Mitochondria in the human embryo are inherited overwhelmingly from the egg, making both statements correct.
Q104. The expansion of CRISPR includes which phrase?
[SSC MTS — Practice]
- (a) Chromosomal Repair in Special Prokaryotes
- (b) Central RNA-Integrated Protein Repair System
- (c) Circular Repeated Information Sequence Process
- (d) Clustered Regularly Interspaced Short Palindromic Repeats
Answer: (d) Clustered Regularly Interspaced Short Palindromic Repeats
Explanation: CRISPR stands for Clustered Regularly Interspaced Short Palindromic Repeats. These repeated DNA elements were first studied within microbial defence systems. Engineered CRISPR systems now provide tools for changing, regulating and detecting nucleic-acid sequences.
Q103. An “off-target effect” in genome editing occurs when:
[RRB NTPC — Practice]
- (a) A plant grows toward sunlight
- (b) PCR is performed at the target temperature
- (c) The editing machinery alters an unintended DNA location
- (d) A gene undergoes normal transcription
Answer: (c) The editing machinery alters an unintended DNA location
Explanation: Off-target editing means a nuclease or editing system modifies a sequence other than the intended target. Similar DNA sequences can sometimes be recognised inadvertently. Careful guide design and independent validation reduce, but may not completely eliminate, this risk.
Q102. Compared with a conventional Cas9 double-strand break, a base editor is designed primarily to:
[RRB Group D — Practice]
- (a) Duplicate every chromosome
- (b) Change selected bases without necessarily cutting both DNA strands
- (c) Destroy all cellular RNA
- (d) Remove the cell nucleus
Answer: (b) Change selected bases without necessarily cutting both DNA strands
Explanation: Base editing couples a targeting protein with a chemical editing activity that can convert particular bases. Many designs avoid deliberate double-strand breaks. Editing windows, bystander changes and off-target activity nevertheless require careful assessment.
Q101. The names Bollgard I and Bollgard II refer primarily to genetically modified varieties of which crop?
[UPSC CSE (Pre) 2021]
- (a) Cotton
- (b) Mustard
- (c) Rice
- (d) Wheat
Answer: (a) Cotton
Explanation: Bollgard technologies are associated with insect-resistant Bt cotton. Bollgard I used a Cry toxin gene, while Bollgard II added another Cry gene to broaden protection against certain bollworms. The introduced proteins originated from Bacillus thuringiensis.
