Which of the following is NOT a component of the PCR reaction mixture?
Answer: D
Restriction enzymes are used in DNA cloning and digestion, not in PCR. PCR requires template DNA, primers, dNTPs, Taq polymerase, and buffer.
Q.22Easy
In DNA sequencing by Sanger method, what role do ddNTPs play?
Answer: B
ddNTPs (dideoxynucleotides) lack a 3'-OH group, causing chain termination when incorporated, generating DNA fragments of different lengths for sequencing.
Q.23Medium
Real-time PCR differs from conventional PCR in that it:
Answer: B
Real-time or qPCR (quantitative PCR) monitors DNA amplification in real-time using fluorescent dyes (SYBR Green or TaqMan probes) to detect product accumulation during each cycle.
Q.24Medium
Which annealing temperature is most appropriate for primers with a GC content of 50%?
Answer: B
Annealing temperature is typically 3-5°C below the Tm (melting temperature). For 50% GC content, Tm ≈ 55-60°C, making this the appropriate annealing range.
Q.25Medium
In next-generation sequencing (NGS), what is the primary advantage of massively parallel sequencing over conventional Sanger sequencing?
Answer: A
NGS provides massively parallel sequencing, generating millions of reads simultaneously, offering significantly lower cost per base and much higher throughput compared to Sanger sequencing.
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Q.26Medium
What is the purpose of using a 'hot start' Taq polymerase in PCR?
Answer: B
Hot start Taq polymerase is inactive at room temperature and becomes activated only at high temperatures (95°C), preventing unwanted non-specific amplification during setup.
Q.27Medium
In DNA barcoding for species identification, which gene region is most commonly used?
Answer: B
COI (cytochrome c oxidase I) is the standard DNA barcode for animal identification due to its high interspecific variation and low intraspecific variation.
Q.28Medium
Which of the following best describes the principle of digital PCR (dPCR)?
Answer: B
Digital PCR partitions the sample into thousands of individual reactions (droplets), allowing absolute quantification by counting positive and negative partitions without requiring standard curves.
Q.29Medium
In gene therapy, AAV (Adeno-associated virus) vectors are preferred because they:
Answer: B
AAVs are preferred due to minimal immunogenic response, ability to target specific tissues, and safe integration properties, despite a packaging limit of ~4.7 kb.
Q.30Medium
What is the principle behind site-directed mutagenesis using PCR?
Answer: B
Site-directed mutagenesis uses primers with mismatches at the desired mutation site. During PCR extension, the mutated sequence is copied, incorporating the specific change.
Q.31Hard
In forensic DNA analysis, STR (Short Tandem Repeat) profiling is preferred over SNPs because:
Answer: B
STRs (variable number tandem repeats) show higher allelic variation than SNPs, providing greater discrimination power for individual identification in forensic cases.
Q.32Hard
Which technique combines PCR with capillary electrophoresis for high-resolution DNA fragment analysis?
Answer: B
Microsatellite (STR) genotyping uses PCR followed by capillary electrophoresis for precise size determination of amplified fragments for forensic and population studies.
Q.33Hard
In the context of 2024-25 genomic studies, what is the primary advantage of long-read sequencing technologies (PacBio, Oxford Nanopore) over short-read NGS?
Answer: C
Long-read sequencing can span repetitive sequences and detect large structural variations that short-reads cannot resolve, improving genome assembly quality.
Q.34Hard
What is the significance of the primer Tm (melting temperature) in multiplex PCR?
Answer: A
In multiplex PCR, all primers should have similar Tm values (within 1-2°C) to use a single annealing temperature, preventing preferential amplification of certain targets.
Q.35Hard
CRISPR-Cas12 (Cpf1) differs from Cas9 in that it:
Answer: B
Cas12 creates staggered cuts resulting in sticky ends, requires only one CRISPR RNA (not separate tracrRNA), and recognizes T-rich PAM sequences, offering advantages for some applications.
Q.36Hard
In environmental metagenomic studies using 16S/18S rRNA amplicon sequencing, what is the primary limitation?
Answer: B
While 16S/18S rRNA is excellent for community profiling, limited sequence divergence at species level makes species-level discrimination challenging, requiring shotgun metagenomics for finer resolution.
Q.37Hard
In somatic gene therapy using ex vivo approach, which cell type is most commonly targeted for genetic modification?
Answer: B
Hematopoietic stem cells are preferred because they can self-renew, are easily accessible via bone marrow/blood, and can be reinfused to establish long-term therapeutic effects for blood disorders.
Q.38Easy
During PCR amplification, which enzyme synthesizes new DNA strands by reading the template DNA in the 3' to 5' direction?
Answer: B
Taq DNA Polymerase (thermostable polymerase from Thermus aquaticus) is the standard enzyme used in PCR. It synthesizes DNA by adding nucleotides to the 3'-OH group of the growing strand.
Q.39Easy
What is the typical temperature range for the annealing step in a standard PCR cycle?
Answer: A
The annealing temperature typically ranges from 50-65°C and depends on the primer's melting temperature (Tm). This allows primers to bind specifically to complementary sequences on the template DNA.
Q.40Easy
In real-time PCR (qPCR), which fluorescent dye binds directly to double-stranded DNA and is most commonly used in 2024-25 diagnostics?
Answer: A
SYBR Green intercalates into double-stranded DNA and fluoresces. It is cost-effective and widely used in qPCR for gene expression studies and viral load detection.
