In real-time PCR (qPCR), which fluorescent dye binds to double-stranded DNA and is commonly used for target quantification?
Answer: A
SYBR Green intercalates into double-stranded DNA and exhibits enhanced fluorescence, making it ideal for real-time monitoring of PCR amplification.
Q.82Easy
What is the theoretical maximum amplification of a DNA segment after 30 PCR cycles?
Answer: B
Each PCR cycle doubles the DNA amount (exponential amplification). After 30 cycles, theoretical amplification = 2^30 ≈ 10^9 fold increase.
Q.83Medium
Which PCR variant would be most suitable for amplifying DNA from degraded or partially degraded samples such as archaeological or forensic specimens?
Answer: C
Degraded DNA has broken fragments; amplifying short segments (<200 bp) increases success rate compared to long-range PCR which requires intact template.
Q.84Medium
In AFLP (Amplified Fragment Length Polymorphism) analysis, what are the two restriction enzymes typically used?
Answer: B
AFLP uses a rare cutter (EcoRI) and frequent cutter (MseI) to generate polymorphic fragments that are amplified using selective PCR.
Q.85Medium
What is the primary disadvantage of using conventional PCR for pathogen detection in clinical diagnostics compared to real-time PCR?
Answer: B
Conventional PCR provides only end-point detection via gel electrophoresis, lacking real-time kinetic data. qPCR enables quantification during amplification and reduces post-PCR work.
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Q.86Hard
In droplet digital PCR (ddPCR), the sample is partitioned into thousands of micro-compartments. What is the primary advantage of this approach?
Answer: B
ddPCR partitions samples into independent reactions, allowing Poisson distribution analysis for absolute quantification without reference standards.
Q.87Hard
Which DNA technology would be most appropriate for detecting point mutations and SNPs in cancer genomics?
Answer: C
NGS and allele-specific digital PCR can detect rare mutations (ctDNA) with high sensitivity; RFLP/DGGE are less sensitive for point mutation detection.
Q.88Medium
In the context of human disease diagnosis, what does the Ct value (Cycle threshold) in qPCR represent?
Answer: B
Ct is the cycle at which fluorescence surpasses background, inversely correlating with initial template amount. Lower Ct = higher initial DNA quantity.
Q.89Medium
Which DNA fingerprinting technique using PCR amplification of repetitive sequences is widely used in paternity testing and criminal investigations in India?
Answer: B
STR profiling amplifies variable number tandem repeats (VNTRs) and is the gold standard for DNA fingerprinting in forensics, recognized by Indian law enforcement and courts.
Q.90Hard
What is the primary challenge in developing universal primers for metagenomic studies of microbial communities?
Answer: B
Universal primers (e.g., 16S rRNA) must accommodate sequence variations across taxa while maintaining specificity, creating a design dilemma.
Q.91Medium
In homozygous versus heterozygous allele detection using allele-specific PCR, which outcome indicates a heterozygous genotype?
Answer: A
Heterozygotes carry both alleles; separate allele-specific primer sets each amplify their respective allele, showing amplification in both reactions.
Q.92Hard
Which modification to standard PCR allows amplification of extremely long DNA fragments (>3 kb)?
Answer: B
Long-range PCR requires thermostable polymerases with 3'→5' exonuclease activity (e.g., Pfu, Phusion) and extended elongation times for processivity.
Q.93Medium
In the context of environmental microbiology, what does PCR-DGGE (Denaturing Gradient Gel Electrophoresis) primarily assess?
Answer: B
PCR-DGGE separates PCR amplicons based on melting behavior, providing a fingerprint of microbial community structure independent of culture.
Q.94Hard
Which PCR-based technique would be most suitable for detecting mutations associated with antibiotic resistance in Mycobacterium tuberculosis in clinical samples?
Answer: B
Allele-specific qPCR can rapidly detect known resistance mutations (e.g., rpoB in rifampicin resistance) in clinical TB samples for faster diagnosis.
Q.95Hard
In the amplification of GC-rich genomic regions, which strategy is most effective to reduce secondary structure formation?
Answer: B
GC-rich regions form hairpins; additives (DMSO/betaine) destabilize secondary structures, while higher denaturation temperatures and specialized polymerases enhance amplification.
Q.96Easy
What is the primary role of dNTPs (deoxynucleotide triphosphates) in the PCR reaction mixture?
Answer: A
dNTPs (dATP, dGTP, dCTP, dTTP) are incorporated into the growing DNA strand by Taq polymerase via phosphodiester bond formation.
Q.97Medium
In next-generation sequencing library preparation, why is PCR amplification of adaptor-ligated DNA fragments critical?
Answer: C
NGS requires substantial DNA; PCR amplifies adaptor-ligated fragments while incorporating index sequences for multiplexing, enabling efficient library preparation.
Q.98Medium
During PCR amplification, the annealing temperature is set based on the Tm (melting temperature) of primers. If primers with Tm of 58°C and 62°C are used in the same reaction, what would be the optimal annealing temperature to ensure efficient amplification of both targets?
Answer: B
The optimal annealing temperature should be set at or slightly below the Tm of the primer with the lowest Tm (58°C) to prevent primer dissociation while maintaining specificity. Using 58°C ensures both primers can bind efficiently.
Q.99Hard
A researcher is performing digital PCR (dPCR) for absolute quantification of mutant KRAS alleles in circulating tumor DNA (ctDNA). Compared to conventional qPCR, what is the primary advantage of dPCR in this application?
Answer: B
Digital PCR partitions samples into thousands of individual reactions, enabling absolute quantification without standard curves. This is crucial for detecting rare mutations where ctDNA comprises only 0.01-1% of total circulating DNA, making it superior for cancer diagnostics.
Q.100Medium
In a multiplex PCR assay designed to simultaneously amplify 6 different STR (short tandem repeat) loci for forensic DNA profiling, what is the critical consideration that must be addressed?
Answer: A
In multiplex PCR, primers with similar Tm values ensure equal amplification efficiency across all targets. Amplicons of comparable sizes prevent preferential amplification of shorter fragments (which amplify faster), ensuring balanced and accurate STR profiles for individual identification.
